Mercurial > docs > diploma

annotate thesis/tex/4-MasqmailsFuture.tex @ 185:1611abd5443b

Find changesets by keywords (author, files, the commit message), revision number or hash, or revset expression.
restructuring and new content (a large commit)
author meillo@marmaro.de
date Mon, 29 Dec 2008 14:06:50 +0100
parents e35c7962d84f
children 7f4d97584a6f
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
rev   line source
109
de590ff06051 changes suggested by schaeffter
meillo@marmaro.de
parents: 99
diff changeset
1 \chapter{\masqmail's present and future}
93
a6f8a93abd64 new chapter 4 (split ch5); added lots of annotations
meillo@marmaro.de
parents:
diff changeset
2
185
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
3 This chapter \dots %fixme write text here
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
4
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
5
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
6
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
7
137
c60b164bfd3c rearranging of ch04
meillo@marmaro.de
parents: 133
diff changeset
8 \section{Existing code base}
185
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
9
142
1b0ba5151d1b person names in small caps
meillo@marmaro.de
parents: 140
diff changeset
10 Here regarded is version 0.2.21 of \masqmail. This is the last version released by Oliver \person{Kurth}, and the basis for my thesis.
1b0ba5151d1b person names in small caps
meillo@marmaro.de
parents: 140
diff changeset
11
132
a83a29e10b10 new books
meillo@marmaro.de
parents: 129
diff changeset
12
185
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
13 \subsubsection*{The source code}
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
14
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
15 \masqmail\ is written in the C programming language. The program, as of version 0.2.21, consists of 34 source code and eight header files, containing about 9,000 lines of code\footnote{Measured with \name{sloccount} by David A.\ Wheeler.}. Additionally, it includes a \name{base64} implementation (about 300 lines) and \name{md5} code (about 150 lines). For systems that do not provide \name{libident}, this library is distributed as well (circa 600 lines); an available shared library however has higher precedence in linking.
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
16
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
17 The only mandatory dependency is \name{glib}---a cross-platform software utility library, originated in the \NAME{GTK+} project. It provides safer replacements for many standard library functions. It also offers handy data containers, easy-to-use implementations of data structures, and much more.
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
18
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
19 With \masqmail\ comes the small tool \path{mservdetect}; it helps setting up a configuration that uses the \name{mserver} system to detect the online state. Two other binaries get compiled for testing purposes: \path{readtest} and \path{smtpsend}. All three programms use \masqmail\ source code; they only add a file with a \verb+main()+ function each.
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
20
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
21 \masqmail\ does not provide an interface to plug in modules with additional functionality. There exists no add-on or module system. The code is only separated by function to the various source files. Some functional parts can be included or excluded by defining symbols. Adding maildir support at compile time, means giving the option \verb+--enable-maildir+ to the \path{configure} call. This preserves the concerning code to get removed by the preprocessor. Unfortunately the \verb+#ifdef+s are scattered through all the source, leading to source code that is hard to read.
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
22 %fixme: refer to ifdef-considered-harmful ?
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
23
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
24
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
25
137
c60b164bfd3c rearranging of ch04
meillo@marmaro.de
parents: 133
diff changeset
26 \subsubsection*{Features}
c60b164bfd3c rearranging of ch04
meillo@marmaro.de
parents: 133
diff changeset
27
142
1b0ba5151d1b person names in small caps
meillo@marmaro.de
parents: 140
diff changeset
28 \masqmail\ accepts mail on the command line and via \SMTP. Mail queueing and alias expansion is supported. \masqmail\ is able to deliver mail to local mailboxes (in \name{mbox} or \name{maildir} format) or pass it to a \name{mail delivery agent} (like \name{procmail}). Mail destinated to remote locations is sent using \SMTP\ or can be piped to commands, being gatesways to \NAME{UUCP} or \NAME{FAX} for example.
132
a83a29e10b10 new books
meillo@marmaro.de
parents: 129
diff changeset
29
142
1b0ba5151d1b person names in small caps
meillo@marmaro.de
parents: 140
diff changeset
30 Outgoing \SMTP\ connections feature \SMTP-\NAME{AUTH} and \SMTP-after-\NAME{POP} authentication, but incoming connections do not. Using wrappers for outgoing connections is supported. This offers a two way communication through a wrapper application like \name{openssl}.
137
c60b164bfd3c rearranging of ch04
meillo@marmaro.de
parents: 133
diff changeset
31 %todo: what about SSL/TLS encryption?
132
a83a29e10b10 new books
meillo@marmaro.de
parents: 129
diff changeset
32
142
1b0ba5151d1b person names in small caps
meillo@marmaro.de
parents: 140
diff changeset
33 \masqmail\ focuses on non-permanent online connections, thus a concept of online routes is used. One may configure any amount of routes to send mail. Each route can have criterias, like matching \texttt{From:} or \texttt{To:} headers, to determine if mail is allowed to be sent using it. Mail to destinations outside the local net gets queued until \masqmail\ is informed about the existance of a online connection.
1b0ba5151d1b person names in small caps
meillo@marmaro.de
parents: 140
diff changeset
34
137
c60b164bfd3c rearranging of ch04
meillo@marmaro.de
parents: 133
diff changeset
35 The \masqmail\ executable can be called under various names for sendmail-compatibility reasons. This is organized by symbolic links with different names pointing to the \masqmail\ executable. The \sendmail\ names are \path{/usr/lib/sendmail} and \path{/usr/sbin/sendmail} because many programs expect the \mta\ to be located there. Further more \sendmail\ supports calling it with a different name instead of supplying command line arguments. The best known of this shortcuts is \path{mailq}, which is equivilent to calling it with the argument \verb+-bq+. \masqmail\ recognizes the names \path{mailq}, \path{smtpd}, \path{mailrm}, \path{runq}, \path{rmail}, and \path{in.smtpd}. The first two are inspired by \sendmail. Not implemented is the name \path{newaliases} because \masqmail\ does not generate binary representations of the alias file.\footnote{A shell script located named \path{newaliases}, that invokes \texttt{masqmail -bi}, can provide the command to satisfy other software needing it.} \path{hoststat} and \path{purgestat} are missing for sendmail-compatibility.
c60b164bfd3c rearranging of ch04
meillo@marmaro.de
parents: 133
diff changeset
36 %masqmail: mailq, mailrm, runq, rmail, smtpd/in.smtpd
c60b164bfd3c rearranging of ch04
meillo@marmaro.de
parents: 133
diff changeset
37 %sendmail: hoststat, mailq, newaliases, purgestat, smtpd
132
a83a29e10b10 new books
meillo@marmaro.de
parents: 129
diff changeset
38
137
c60b164bfd3c rearranging of ch04
meillo@marmaro.de
parents: 133
diff changeset
39 Additional to the \mta\ job, \masqmail\ also offers mail retrieval services with being a \NAME{POP3} client. It can fetch mail from different remote locations, dependent on the active online route.
132
a83a29e10b10 new books
meillo@marmaro.de
parents: 129
diff changeset
40
a83a29e10b10 new books
meillo@marmaro.de
parents: 129
diff changeset
41
a83a29e10b10 new books
meillo@marmaro.de
parents: 129
diff changeset
42
a83a29e10b10 new books
meillo@marmaro.de
parents: 129
diff changeset
43
a83a29e10b10 new books
meillo@marmaro.de
parents: 129
diff changeset
44
a83a29e10b10 new books
meillo@marmaro.de
parents: 129
diff changeset
45
177
7781ad0811f7 new sections, moved content, and more
meillo@marmaro.de
parents: 173
diff changeset
46 \section{Requirements}
146
2c4673d983c3 wrote about requirements (related to directions to go)
meillo@marmaro.de
parents: 142
diff changeset
47
185
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
48 This section identifies the requirements for a modern \masqmail. Most of them will apply to modern \MTA{}s in general.
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
49
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
50
177
7781ad0811f7 new sections, moved content, and more
meillo@marmaro.de
parents: 173
diff changeset
51
7781ad0811f7 new sections, moved content, and more
meillo@marmaro.de
parents: 173
diff changeset
52 \subsection{General requirements}
146
2c4673d983c3 wrote about requirements (related to directions to go)
meillo@marmaro.de
parents: 142
diff changeset
53
185
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
54 The following list of general requirements applies not only to \masqmail, but to all kinds of programs in similar environment doing similar jobs with the same intention. These requirements can be covered by the term ``quality''.
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
55 %fixme: add cites
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
56 %fixme: refer to ch01 and ch02
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
57 General requirements specify the non-functional properties of the software, thus they are also called \name{non-functional requirements}.
146
2c4673d983c3 wrote about requirements (related to directions to go)
meillo@marmaro.de
parents: 142
diff changeset
58
137
c60b164bfd3c rearranging of ch04
meillo@marmaro.de
parents: 133
diff changeset
59
177
7781ad0811f7 new sections, moved content, and more
meillo@marmaro.de
parents: 173
diff changeset
60 \subsubsection*{Security}
7781ad0811f7 new sections, moved content, and more
meillo@marmaro.de
parents: 173
diff changeset
61 \MTA{}s are critical points for computer security, as they are accessable from external networks. They must be secured with high effort. Properties like high priviledge level, work load influenced from extern, work on unsafe data, and demand for reliability, increase the security needed. Unsecure and unreliable \mta{}s are of no value. \masqmail\ needs to b e secure enough for its target field of operation.
7781ad0811f7 new sections, moved content, and more
meillo@marmaro.de
parents: 173
diff changeset
62
7781ad0811f7 new sections, moved content, and more
meillo@marmaro.de
parents: 173
diff changeset
63
7781ad0811f7 new sections, moved content, and more
meillo@marmaro.de
parents: 173
diff changeset
64 \subsubsection*{Reliability}
7781ad0811f7 new sections, moved content, and more
meillo@marmaro.de
parents: 173
diff changeset
65 << crash only software >>
7781ad0811f7 new sections, moved content, and more
meillo@marmaro.de
parents: 173
diff changeset
66
7781ad0811f7 new sections, moved content, and more
meillo@marmaro.de
parents: 173
diff changeset
67 << dont lose mail >>
7781ad0811f7 new sections, moved content, and more
meillo@marmaro.de
parents: 173
diff changeset
68
7781ad0811f7 new sections, moved content, and more
meillo@marmaro.de
parents: 173
diff changeset
69
7781ad0811f7 new sections, moved content, and more
meillo@marmaro.de
parents: 173
diff changeset
70 \subsubsection*{Extendability}
7781ad0811f7 new sections, moved content, and more
meillo@marmaro.de
parents: 173
diff changeset
71 Modern needs like large messages demand for more efficient mail transport through the net. Aswell is a final solution needed to defeat the spam problem. New mail transport protocols seem to be the only good solutions for both problems. They also can improve reliability, authentication, and verification issues. \masqmail\ should be able to support new mail transfer protocols as they appear and are used.
7781ad0811f7 new sections, moved content, and more
meillo@marmaro.de
parents: 173
diff changeset
72 %fixme: like old sendmail, but not too much like it
146
2c4673d983c3 wrote about requirements (related to directions to go)
meillo@marmaro.de
parents: 142
diff changeset
73
2c4673d983c3 wrote about requirements (related to directions to go)
meillo@marmaro.de
parents: 142
diff changeset
74
2c4673d983c3 wrote about requirements (related to directions to go)
meillo@marmaro.de
parents: 142
diff changeset
75 \subsubsection*{Ressource friendly software}
149
ccf0de1ae337 new content and rework
meillo@marmaro.de
parents: 146
diff changeset
76 The merge of communication hardware and the move of email services from providers to homes, demands smaller and more resource-friendly software. The amount of mail will be lower, even if much more mail will be sent. More important will be the energy consumption and heat emission. These topics increased in relevance during the past years and they are expected to become more central. \masqmail\ is not a program to be used on large servers, but to be used on small devices. Thus focusing on energy and heat, not on performance, is the direction to go.
132
a83a29e10b10 new books
meillo@marmaro.de
parents: 129
diff changeset
77
a83a29e10b10 new books
meillo@marmaro.de
parents: 129
diff changeset
78
146
2c4673d983c3 wrote about requirements (related to directions to go)
meillo@marmaro.de
parents: 142
diff changeset
79 \subsubsection*{Easy configuration}
149
ccf0de1ae337 new content and rework
meillo@marmaro.de
parents: 146
diff changeset
80 Having \mta{}s on many home servers and clients, requires easy and standardized configuration. The common setups should be configurable with single actions by the user. Complex configuration should be possible, but focused must be the most common form of configuration: choosing one of several standard setups.
146
2c4673d983c3 wrote about requirements (related to directions to go)
meillo@marmaro.de
parents: 142
diff changeset
81
2c4673d983c3 wrote about requirements (related to directions to go)
meillo@marmaro.de
parents: 142
diff changeset
82
2c4673d983c3 wrote about requirements (related to directions to go)
meillo@marmaro.de
parents: 142
diff changeset
83
2c4673d983c3 wrote about requirements (related to directions to go)
meillo@marmaro.de
parents: 142
diff changeset
84
137
c60b164bfd3c rearranging of ch04
meillo@marmaro.de
parents: 133
diff changeset
85
146
2c4673d983c3 wrote about requirements (related to directions to go)
meillo@marmaro.de
parents: 142
diff changeset
86
185
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
87
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
88 \subsection{Functional requirements}
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
89
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
90 This section identifies the needed functionality for a modern \MTA. The basic job of a \mta\ is to tranport mail from a sender to a recipient. This is the definition of such kind of software and this is how \MTA{}s are generally seen \cite[page 19]{dent04} \cite[pages 3-5]{hafiz05}.
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
91
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
92 An \MTA\ therefore needs at least a mail receiving facility and a mail sending facility.
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
93
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
94
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
95
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
96 \subsubsection*{Incoming channels}
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
97
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
98 \sendmail-compatible \mta{}s must support at least two incoming channels: mail submitted using the \sendmail\ command, and mail received via the \SMTP\ daemon. Thus it is common to split the incoming channel into local and remote. This is done by \qmail\ and \postfix. The same way is \person{Hafiz}'s view. \SMTP\ is the primary mail transport protocol today, but with the increasing need for new protocols\ref{FIXME} in mind, support for more than just \SMTP\ is good to have. This leads to more than one remote channel.
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
99
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
100
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
101 \subsubsection*{Outgoing channels}
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
102
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
103 Outgoing mail is commonly either sent using \SMTP, piped into local commands (for example \texttt{uucp}), or delivered locally by appending to a mailbox.
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
104
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
105 Outgoing channels are similar for \qmail, \postfix, and \name{sendmail X}: All of them have a module to send mail using \SMTP, and one for writing into a local mailbox. Local mail delivery is a job that requires root priveledge to be able to switch to any user in order to write to his mailbox.
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
106
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
107 As mail delivery to local users, is \emph{not} included in the basic job of an \MTA{}, why should it care about it? In order to keep the system simple and to have programs that do one job well, the local delivery job should be handed over to a specialist: the \name{mail delivery agent}. \NAME{MDA}s know about the various mailbox formats and are aware of the problems of concurrent write access and thelike. Hence handling the message and the responsiblity over to a \NAME{MDA}, like \name{procmail} or \name{maildrop}, seems to be the right way to go.
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
108
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
109 This means an outgoing connection that pipes mail into local commands is required. Other outgoing channels, one for each supportet protocol, may be designed like it was done in other \MTA{}s.
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
110
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
111
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
112
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
113 \subsubsection*{Mail queue}
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
114
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
115 Additionally to the mail receiving and sending facilities, mail queues are a basic feature. A mail queue removes the need to deliver intantly as a message is received. They provide fail-safe storage of mails until they are delivered. Mail queues are probably used in all \mta{}s, excluding the simple forwarders. A mail queue is a essential requirement for \masqmail, as it is to be used for non-permanent online connections. This means, mail must be queued until a online connection is available to send the message.
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
116
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
117 The mail queue and the module to manage it are the central part of the whole system. This demands especially for robustness and reliability, as a failure here can lead to loosing mail. An \MTA\ takes over responsibility for mail in accepting it, hence loosing mail messages is absolutely to avoid. This covers any kind of crash situation too. The worst thing acceptable to happen is a mail to be sent twice.
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
118
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
119 \sendmail, \exim, \qmail, \name{sendmail X}, and \masqmail\ feature one single mail queue. \postfix\ has three of them: \name{incoming}, \name{active}, and \name{deferred}. (The \name{maildrop} queue is excluded, as it is only used for the \texttt{sendmail} command.)
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
120
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
121 \MTA\ setups that do external content scanning tend to require two separate queues. To use \sendmail\ in such setups requires two independent instances, with two separate queues, running. \exim\ can handle it with special \name{router} and \name{transport} rules, but the data flow gets complicated. Having two independent queues seems to be preferable.
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
122
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
123
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
124
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
125
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
126 \subsubsection*{Header sanitizing}
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
127
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
128 Mail coming into the system often lacks important header lines. At least the required ones must be added from the \MTA. One example is the \texttt{Date:} header, another is the, not required but recommended \texttt{Message-ID:} header. Apart from adding missing headers, rewriting headers is important too, to change the locally known domain part of email addresses to globally known ones for example. \masqmail\ needs also the ability to rewrite the domain part dependent on the route used to send the message.
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
129
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
130 Generating the envelope is a related job. The envelope specifies the actual recipient of the mail, no matter what the \texttt{To:}, \texttt{Cc:}, and \texttt{Bcc:} headers tell. Multiple reciptients lead to multiple different envelopes, containing all the same mail message.
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
131
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
132
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
133
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
134
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
135 \subsubsection*{Aliasing}
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
136
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
137 Email addresses can have aliases and need to be expanded. Aliases can be of different kind: different local user, remote user, list of local and/or remote users, or a command. Most important are the aliases in the \path{aliases} file, usually located at \path{/etc/aliases}. Addresses expanding to lists of users lead to more envelopes. Aliases changing the reciptients domain part may require a different route to use.
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
138
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
139
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
140
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
141
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
142 \subsubsection*{Choose route to use}
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
143
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
144 One key feature of \masqmail\ is its ability to send mail out in different ways. The decision is based on the current online state and whether a route may be used for a message or not. The online state can be retrieved in tree ways, explained in \ref{sec:fixme}. A route to send is found by checking every available route for being able to transfer the current message, until one matches.
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
145
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
146
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
147
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
148
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
149 \subsubsection*{Authentication}
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
150
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
151 One thing to avoid is being an \name{open relay}. Open relays allow to relay mail from everywhere to everywhere. This is a major source of spam. The solution is restricting relay\footnote{Relaying is passing mail, that is not from and not for the own system, through it.} access.
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
152
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
153 Several ways to restrict access are available. The most simple one is restrictiction relaying by the \NAME{IP} address. No extra complexity is added this way, but static \NAME{IP} addresses are needed.
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
154
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
155 If static access restriction is not possible, for example mail from locations with changing \NAME{IP} addresses, some kind of authentication mechanism is required. Three common kinds exist:
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
156 \begin{itemize}
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
157 \item \SMTP-after-\NAME{POP}: Uses authenication on the \NAME{POP} protocol to permit incoming \SMTP\ connections for a limited time afterwards.
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
158 \item \SMTP authentication: An extension to \SMTP. Authentication can be requested before mail is accepted.
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
159 \item Certificates: They confirm the identity of someone.
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
160 \end{itemize}
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
161
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
162
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
163
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
164 \subsubsection*{Encryption}
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
165
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
166 Electronic mail is very weak to sniffing attacks, because all data transfer is unencrypted. This concerns the message's content, as well as the email addresses in header and envelope, but also authentication dialogs that may transfer plain text passwords (\NAME{PLAIN} and \NAME{LOGIN} are examples). Thus encryption is wanted.
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
167
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
168 The common way to encrypt \SMTP\ dialogs is using \name{Transport Layer Security} (short: \TLS, successor of \NAME{SSL}). \TLS\ encrypts the datagrams of the \name{transport layer}. This means it works below the application protocols and can be used by any of them\citeweb{wikipedia:tls}.
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
169
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
170 Outgoing \SMTP\ connections can get encrypted using a secure tunnel, created by an external application. Incoming connections, can not use this technique because the remote \NAME{IP} address is hidden then; \NAME{STARTTLS}---defined in \RFC2487---is what \mta{}s implement.
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
171
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
172
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
173
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
174 \subsubsection*{Spam prevention}
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
175
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
176 Spam is a major threat nowadays, but it is a war in which the good guys tend to lose. Putting much effort in fighting spam results in few gain. Real success will only be possible with new---better---protocols and abandonning the weak legacy technologies. The goal is to provide state-of-the-art spam protection, but not more (see section \ref{sec:swot-analysis}). As spam is not just a nuisance for end users, but also for the infrastructure---the \mta{}s---by increasing the amount of mail messages, \MTA{}s need to protect themself.
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
177
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
178 Filtering spam can be done in two ways: Refusing spam during the \SMTP\ dialog or checking for spam after the mail was accepted and queued. Both have advantages and disadvantages, so modern \MTA{}s use them in combination. Spam is identified by the results of a set of checks. Static rules, querying databases (\NAME{DNS} blacklists), requesting special client behavior (\name{greylisting}, \name{hashcash}), or statistical analysis (\name{bogofilter}) are checks that may be used. Running more checks leads to better results, but takes more system resources and time.
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
179
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
180 Doing some basic checks during the \SMTP\ dialog seems to be a must.
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
181
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
182
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
183
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
184 \subsubsection*{Virus checking}
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
185
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
186 Related to spam is malicous content (short: \name{malware}) like viruses, worms, trojan horses. They, in contrast to spam, do not affect the \MTA\ itself, as they are in the mail body. \MTA{}s searching for malware is equal to real world's post offices opening letters to check if they contain something that could harm the recipient. This is not a mail transport job. But the last \MTA---the one responsible for the recipient---seems to be at a good position to do this work.
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
187
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
188 In any way should malware checking be done by external programs that may be invoked by the \mta. But using mail deliver and processing agents, like \name{procmail}, a better suited locations to invoke content scanners.
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
189
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
190 A popular email filter framework is \name{amavis} which integrates various spam and virus scanners. The common setup includes a receiving \MTA\ which sends it to \name{amavis} using \SMTP, \name{amavis} processes the mail and sends it then to a second \MTA\ that does the outgoing transfer. Having interfaces to such scanners is, for sure, good to have.
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
191
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
192
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
193
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
194 \subsubsection*{Archiving}
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
195
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
196 Mail archiving and auditability become more important as electronic mail becomes more important. The ability to archive verbatim copies of every mail coming into and every mail going out of the system, with relation between them, appears to be a goal to achieve.
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
197
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
198 \postfix\ for example has a \texttt{always\_bcc} feature, to send a copy of every mail to a definable reciptient. At least this funtionality should be given, although a more complete approach is preferable.
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
199
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
200
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
201
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
202
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
203
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
204
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
205
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
206
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
207 \section{Work to do}
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
208
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
209 What exists, what is missing, what needs to be done?
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
210
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
211 auth, enc, archiving
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
212
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
213 \masqmail\ is already able to encrypt outgoing connections, but encryption of incoming connections, using \NAME{STARTTLS} should be implemented. This only affects the \SMTP\ server module.
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
214
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
215
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
216
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
217
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
218 \subsubsection*{Discussion on architecture}
146
2c4673d983c3 wrote about requirements (related to directions to go)
meillo@marmaro.de
parents: 142
diff changeset
219
163
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
220 A program's architecture is probably the most influencing design decision, and has the greatest impact on the program's future capabilities. %fixme: search quote ... check if good
161
18b7b517e2dd wrote about discussion on architecture
meillo@marmaro.de
parents: 155
diff changeset
221
18b7b517e2dd wrote about discussion on architecture
meillo@marmaro.de
parents: 155
diff changeset
222 \masqmail's current artitecture is monolitic like \sendmail's and \exim's. But more than the other two, is it one block of interweaved code. \sendmail\ provides now, with its \name{milter} interface, standardized connection channels to external modules. \exim\ has a highly structured code with many internal interfaces, like the one for supported authentication ``modules''. \masqmail\ has none of them; it is what \sendmail\ was in the beginning: a single large block.
18b7b517e2dd wrote about discussion on architecture
meillo@marmaro.de
parents: 155
diff changeset
223
18b7b517e2dd wrote about discussion on architecture
meillo@marmaro.de
parents: 155
diff changeset
224 Figure \ref{fig:masqmail-arch} is an attempt to depict \masqmail's internal structure.
18b7b517e2dd wrote about discussion on architecture
meillo@marmaro.de
parents: 155
diff changeset
225
18b7b517e2dd wrote about discussion on architecture
meillo@marmaro.de
parents: 155
diff changeset
226 \begin{figure}
18b7b517e2dd wrote about discussion on architecture
meillo@marmaro.de
parents: 155
diff changeset
227 \begin{center}
18b7b517e2dd wrote about discussion on architecture
meillo@marmaro.de
parents: 155
diff changeset
228 \input{input/masqmail-arch.tex}
18b7b517e2dd wrote about discussion on architecture
meillo@marmaro.de
parents: 155
diff changeset
229 \end{center}
18b7b517e2dd wrote about discussion on architecture
meillo@marmaro.de
parents: 155
diff changeset
230 \caption{Internal architecture of \masqmail}
18b7b517e2dd wrote about discussion on architecture
meillo@marmaro.de
parents: 155
diff changeset
231 \label{fig:masqmail-arch}
18b7b517e2dd wrote about discussion on architecture
meillo@marmaro.de
parents: 155
diff changeset
232 \end{figure}
18b7b517e2dd wrote about discussion on architecture
meillo@marmaro.de
parents: 155
diff changeset
233
163
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
234 \sendmail\ improved its old architecture, for example by adding the milter interface. \exim\ was designed and is carefully maintained with a modular-like code structure in mind. \qmail\ started from scratch with a ``security-first'' approach, \postfix\ improved on it, and \name{sendmail X}/\name{MeTA1} tries to adopt the best of \qmail\ and \postfix, to completely replace the old \sendmail\ architecture. \person{Hafiz} \cite{hafiz05}. describes this evolution of \mta\ architecture very well.
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
235
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
236 Every one of the popular \MTA{}s is more modular, or became more modular over time, than \masqmail\ is. Modern requirements like spam protection and future requirements like the use of new mail transport protocols demand modular designs for keeping the software simple. Simplicity is a key property for security.
161
18b7b517e2dd wrote about discussion on architecture
meillo@marmaro.de
parents: 155
diff changeset
237
163
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
238 \person{Hafiz} agrees:
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
239 \begin{quote}
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
240 The goal of making software secure can be better achieved by making the design simple and easier to understand and verify. \cite[page64]{hafiz05}
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
241 \end{quote}
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
242 He identifies the security of \qmail\ to come from it's \name{compartmentalization}, which goes hand in hand with modularity:
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
243 \begin{quote}
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
244 A perfect example is the contrast between the feature envy early \sendmail\ architecture implemented as one process and the simple, modular architecture of \qmail. The security of \qmail\ comes from its compartmentalized simple processes that perform one task only and are therefor testable for security. \cite[page 64]{hafiz05}
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
245 \end{quote}
165
a7fd6d974d3c added lots of notes about spam, malware, auth, ...
meillo@marmaro.de
parents: 163
diff changeset
246 As well does \person{Dent}: ``The modular architecture of Postfix forms the basis for much of its security.''\cite[page 7]{dent04}
163
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
247
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
248 Modularity is needed for supporting modern \MTA\ requirements, providing a clear interface to add further functionality without increasing the overall complexity much. Modularity is also an enabler for security. Security comes from good design, as \person{Graff} and \person{van Wyk} explain:
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
249 \begin{quote}
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
250 Good design is the sword and shield of the security-conscious developer. Sound design defends your application from subversion or misuse, protecting your network and the information on it from internal and external attacks alike. It also provides a safe foundation for future extensions and maintainance of the software.
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
251 %
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
252 %Bad design makes life easier for attackers and harder for the good guys, especially if it contributes to a false sends of security while obscuring pertinent failings.
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
253 \cite[page 55]{graff03}
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
254 \end{quote}
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
255
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
256 \person{Hafiz} adds: ``The major idea is that security cannot be retrofitted into an architecture.''\cite[page 64]{hafiz05}
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
257
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
258 All this leads to one logical step: The rewrite of \masqmail\ using a modern, modular architecture, to get a modern \MTA\ satisfying nowadays needs.
161
18b7b517e2dd wrote about discussion on architecture
meillo@marmaro.de
parents: 155
diff changeset
259
18b7b517e2dd wrote about discussion on architecture
meillo@marmaro.de
parents: 155
diff changeset
260
18b7b517e2dd wrote about discussion on architecture
meillo@marmaro.de
parents: 155
diff changeset
261
185
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
262 \subsubsection*{A design from scratch?}
177
7781ad0811f7 new sections, moved content, and more
meillo@marmaro.de
parents: 173
diff changeset
263
185
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
264 << what would be needed (effort) >>
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
265
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
266 The next section is a design
177
7781ad0811f7 new sections, moved content, and more
meillo@marmaro.de
parents: 173
diff changeset
267
7781ad0811f7 new sections, moved content, and more
meillo@marmaro.de
parents: 173
diff changeset
268
7781ad0811f7 new sections, moved content, and more
meillo@marmaro.de
parents: 173
diff changeset
269
7781ad0811f7 new sections, moved content, and more
meillo@marmaro.de
parents: 173
diff changeset
270
7781ad0811f7 new sections, moved content, and more
meillo@marmaro.de
parents: 173
diff changeset
271
7781ad0811f7 new sections, moved content, and more
meillo@marmaro.de
parents: 173
diff changeset
272
7781ad0811f7 new sections, moved content, and more
meillo@marmaro.de
parents: 173
diff changeset
273
185
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
274 \section{A design from scratch}
163
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
275
185
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
276 The last sections identified the jobs that need to be done by a modern \MTA; problems and prefered choices were mentioned too. Now the various jobs are assigned to modules, of which an architecture is created. It is inpired by existing ones and driven by the identified jobs and requirements.
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
277
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
278
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
279
163
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
280
185
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
281 \subsection{Design decisions}
163
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
282
185
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
283 One major design idea of the design were:
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
284 \begin{itemize}
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
285 \item free the internal system from in and out channels
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
286 \item arbitrary protocol handlers have to be addable afterwards
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
287 \item a single facility for scanning (all mail goes through it)
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
288 \item concentrate on mail transfer
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
289 \end{itemize}
163
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
290
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
291
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
292 \subsubsection*{Incoming channels}
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
293
170
204683bfb4e7 wrote much about modules of an MTA
meillo@marmaro.de
parents: 167
diff changeset
294 \sendmail-compatible \mta{}s must support at least two incoming channels: mail submitted using the \sendmail\ command, and mail received via the \SMTP\ daemon. It is therefor common to split the incoming channel into local and remote. This is done by \qmail\ and \postfix. The same way is \person{Hafiz}'s view.
163
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
295
170
204683bfb4e7 wrote much about modules of an MTA
meillo@marmaro.de
parents: 167
diff changeset
296 In contrast is \name{sendmail X}: Its locally submitted messages go to the \SMTP\ daemon, which is the only connection towards the mail queue. %fixme: is it a smtp dialog? or a second door?
204683bfb4e7 wrote much about modules of an MTA
meillo@marmaro.de
parents: 167
diff changeset
297 \person{fanf} proposes a similar approach. He wants the \texttt{sendmail} command to be a simple \SMTP\ client that contacts the \SMTP\ daemon of the \MTA\ like it is done by connections from remote. The advantage here is one single module where all \SMTP\ dialog with submitters is done. Hence one single point to accept or refuse incoming mail. Additionally does the module to put mail into the queue not need to be \name{setuid} or \name{setgid} because it is only invoked from the \SMTP\ daemon. The \MTA's architecture would become simpler and common tasks are not duplicated in modules that do similar jobs.
163
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
298
170
204683bfb4e7 wrote much about modules of an MTA
meillo@marmaro.de
parents: 167
diff changeset
299 But merging the input channels in the \SMTP\ daemon makes the \MTA\ heavily dependent on \SMTP\ being the main mail transfer protocol. To \qmail\ and \postfix\ new modules to support other ways of message receival may be added without change of other parts of the system. Also is it better to have more independent modules if each one is simpler then.
163
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
300
170
204683bfb4e7 wrote much about modules of an MTA
meillo@marmaro.de
parents: 167
diff changeset
301 With the increasing need for new protocols in mind, it seems better to have single modules for each incoming channel, although this leads to duplicated acceptance checks.
163
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
302
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
303
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
304 \subsubsection*{Outgoing channels}
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
305
170
204683bfb4e7 wrote much about modules of an MTA
meillo@marmaro.de
parents: 167
diff changeset
306 Outgoing mail is commonly either sent using \SMTP, piped into local commands (for example \texttt{uucp}), or delivered locally by appending to a mailbox.
204683bfb4e7 wrote much about modules of an MTA
meillo@marmaro.de
parents: 167
diff changeset
307
163
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
308 Outgoing channels are similar for \qmail, \postfix, and \name{sendmail X}: All of them have a module to send mail using \SMTP, and one for writing into a local mailbox. Local mail delivery is a job that requires root priveledge to be able to switch to any user in order to write to his mailbox. Modular \MTA{}s do not need \name{setuid root}, but the local delivery process (or its parent) needs to run as root.
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
309
170
204683bfb4e7 wrote much about modules of an MTA
meillo@marmaro.de
parents: 167
diff changeset
310 As mail delivery to local users, is \emph{not} included in the basic job of an \MTA{}, why should it care about it? In order to keep the system simple and to have programs that do one job well, the local delivery job should be handed over to a specialist: the \name{mail delivery agent}. \NAME{MDA}s know about the various mailbox formats and are aware of the problems of concurrent write access and thelike. Hence handling the message and the responsiblity over to a \NAME{MDA}, like \name{procmail} or \name{maildrop}, seems to be the right way to go.
204683bfb4e7 wrote much about modules of an MTA
meillo@marmaro.de
parents: 167
diff changeset
311
204683bfb4e7 wrote much about modules of an MTA
meillo@marmaro.de
parents: 167
diff changeset
312 This means an outgoing connection that pipes mail into local commands is required. Other outgoing channels, one for each supportet protocol, may be designed like it was done in other \MTA{}s.
204683bfb4e7 wrote much about modules of an MTA
meillo@marmaro.de
parents: 167
diff changeset
313
204683bfb4e7 wrote much about modules of an MTA
meillo@marmaro.de
parents: 167
diff changeset
314
204683bfb4e7 wrote much about modules of an MTA
meillo@marmaro.de
parents: 167
diff changeset
315
204683bfb4e7 wrote much about modules of an MTA
meillo@marmaro.de
parents: 167
diff changeset
316 \subsubsection*{Mail queue}
163
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
317
170
204683bfb4e7 wrote much about modules of an MTA
meillo@marmaro.de
parents: 167
diff changeset
318 Mail queues are probably used in all \mta{}s, excluding the simple forwarders. A mail queue is a essential requirement for \masqmail, as it is to be used for non-permanent online connections. This means, mail must be queued until a online connection is available to send the message.
204683bfb4e7 wrote much about modules of an MTA
meillo@marmaro.de
parents: 167
diff changeset
319
204683bfb4e7 wrote much about modules of an MTA
meillo@marmaro.de
parents: 167
diff changeset
320 The mail queue and the module to manage it are the central part of the whole system. This demands especially for robustness and reliability, as a failure here can lead to loosing mail. An \MTA\ takes over responsibility for mail in accepting it, hence loosing mail messages is absolutely to avoid. This covers any kind of crash situation too. The worst thing acceptable to happen is a mail to be sent twice.
204683bfb4e7 wrote much about modules of an MTA
meillo@marmaro.de
parents: 167
diff changeset
321
204683bfb4e7 wrote much about modules of an MTA
meillo@marmaro.de
parents: 167
diff changeset
322 \sendmail, \exim, \qmail, \name{sendmail X}, and \masqmail\ feature one single mail queue. \postfix\ has three of them: \name{incoming}, \name{active}, and \name{deferred}. (The \name{maildrop} queue is excluded, as it is only used for the \texttt{sendmail} command.)
204683bfb4e7 wrote much about modules of an MTA
meillo@marmaro.de
parents: 167
diff changeset
323
204683bfb4e7 wrote much about modules of an MTA
meillo@marmaro.de
parents: 167
diff changeset
324 \MTA\ setups that include content scanning tend to require two separate queues. To use \sendmail\ in such setups requires two independent instances, with two separate queues, running. \exim\ can handle it with special \name{router} and \name{transport} rules, but the data flow gets complicated. Hence an idea is to use two queues, \name{incoming} and \name{active} in \postfix's terminology, with the content scanning within the move from \name{incoming} to \name{active}.
163
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
325
182
e35c7962d84f wrote about spool file and permissions
meillo@marmaro.de
parents: 180
diff changeset
326 \sendmail, \exim, \qmail, and \masqmail\ all use at least two files to store one message in the queue: one file contains the message body, another the envelope and header information. The one containing the mail body is not modified at all. \postfix\ takes a different approach in storing queued messages in an internal format within one file. \person{Finch} takes yet another different approach in suggesting to store the whole queue in one single file with pointers to separating positions \cite{finchFIXME}.
e35c7962d84f wrote about spool file and permissions
meillo@marmaro.de
parents: 180
diff changeset
327 %fixme: check, cite, and think about
e35c7962d84f wrote about spool file and permissions
meillo@marmaro.de
parents: 180
diff changeset
328
163
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
329
165
a7fd6d974d3c added lots of notes about spam, malware, auth, ...
meillo@marmaro.de
parents: 163
diff changeset
330
a7fd6d974d3c added lots of notes about spam, malware, auth, ...
meillo@marmaro.de
parents: 163
diff changeset
331 \subsubsection*{Sanitize mail}
170
204683bfb4e7 wrote much about modules of an MTA
meillo@marmaro.de
parents: 167
diff changeset
332
204683bfb4e7 wrote much about modules of an MTA
meillo@marmaro.de
parents: 167
diff changeset
333 Mail coming into the system often lacks important header lines. At least the required ones must be added from the \MTA. A good example is the \texttt{Message-Id:} header.
204683bfb4e7 wrote much about modules of an MTA
meillo@marmaro.de
parents: 167
diff changeset
334
204683bfb4e7 wrote much about modules of an MTA
meillo@marmaro.de
parents: 167
diff changeset
335 In \postfix, this is done by the \name{cleanup} module, which invokes \name{rewrite}. The position in the message flow is after coming from one of the several incoming channels and before the message is stored into the \name{incoming} queue. Modules that handle incoming channels may also add headers, for example the \texttt{From:} and \texttt{Date:} headers. \name{cleanup}, however, does a complete check to make the mail header complete and valid.
204683bfb4e7 wrote much about modules of an MTA
meillo@marmaro.de
parents: 167
diff changeset
336
204683bfb4e7 wrote much about modules of an MTA
meillo@marmaro.de
parents: 167
diff changeset
337 Apart from deciding where to sanitize the mail header, is the question where to generate the envelope. The envelope specifies the actual recipient of the mail, no matter what the \texttt{To:}, \texttt{Cc:}, and \texttt{Bcc:} headers tell. Multiple reciptients lead to multiple different envelopes, containing all the same mail message.
204683bfb4e7 wrote much about modules of an MTA
meillo@marmaro.de
parents: 167
diff changeset
338
165
a7fd6d974d3c added lots of notes about spam, malware, auth, ...
meillo@marmaro.de
parents: 163
diff changeset
339
170
204683bfb4e7 wrote much about modules of an MTA
meillo@marmaro.de
parents: 167
diff changeset
340
165
a7fd6d974d3c added lots of notes about spam, malware, auth, ...
meillo@marmaro.de
parents: 163
diff changeset
341 \subsubsection*{Aliasing}
a7fd6d974d3c added lots of notes about spam, malware, auth, ...
meillo@marmaro.de
parents: 163
diff changeset
342
170
204683bfb4e7 wrote much about modules of an MTA
meillo@marmaro.de
parents: 167
diff changeset
343 Where should aliases get expanded? They appear in different kind. Important are the ones available in the \path{aliases} file. Aliases can be:
204683bfb4e7 wrote much about modules of an MTA
meillo@marmaro.de
parents: 167
diff changeset
344 \begin{itemize}
204683bfb4e7 wrote much about modules of an MTA
meillo@marmaro.de
parents: 167
diff changeset
345 \item a different local user (e.g.\ ``\texttt{bob: alice}'')
204683bfb4e7 wrote much about modules of an MTA
meillo@marmaro.de
parents: 167
diff changeset
346 \item a remote user (e.g.\ ``\texttt{bob: john@example.com}'')
204683bfb4e7 wrote much about modules of an MTA
meillo@marmaro.de
parents: 167
diff changeset
347 \item a list of users (e.g.\ ``\texttt{bob: alice, john@example.com}'')
204683bfb4e7 wrote much about modules of an MTA
meillo@marmaro.de
parents: 167
diff changeset
348 \item a command (e.g.\ ``\texttt{bob: |foo}'')
204683bfb4e7 wrote much about modules of an MTA
meillo@marmaro.de
parents: 167
diff changeset
349 \end{itemize}
204683bfb4e7 wrote much about modules of an MTA
meillo@marmaro.de
parents: 167
diff changeset
350 Addresses expanding to lists of users lead to more envelopes. Aliases changing the reciptients domain part may require a different route to use.
165
a7fd6d974d3c added lots of notes about spam, malware, auth, ...
meillo@marmaro.de
parents: 163
diff changeset
351
172
5c873e6478ef wrote about encryption
meillo@marmaro.de
parents: 170
diff changeset
352 Aliasing is often handled in expanding the alias and reinjecting the mail into the system. Unfortunately, the mail is processed twice then; additionally does the system have to handle more mail this way. If it is wanted to check the new recipient address for acceptance and do all processing again, then reinjecting it is the best choice.
163
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
353
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
354
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
355
185
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
356 \subsubsection*{Choose route to use}
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
357
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
358 One key feature of \masqmail\ is its ability to send mail out in different ways. The decision is based on the current online state and whether a route may be used for a message or not. The online state can be retrieved in tree ways, explained in \ref{sec:fixme}. A route to send is found by checking every available route for being able to transfer the current message, until one matches.
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
359
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
360 This functionality should be implemented in the module that is responsible to invoke one of the outgoing channel modules (for example the one for \SMTP\ or the pipe module).
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
361
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
362 \masqmail\ can rewrite the envelope's from address and the \texttt{From:} header, dependent on the outgoing route to use. This rewrite must be done \emph{after} it is clear which route a mail will take, of course, so this may be not the module where other header editing is done.
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
363 %fixme: see hafiz05 page 57: maybe put the rewriting into the sending module (like smx, exim, courier) (problem with archiving of all outgoing mail?)
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
364
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
365
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
366
163
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
367 \subsubsection*{Authentication}
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
368
170
204683bfb4e7 wrote much about modules of an MTA
meillo@marmaro.de
parents: 167
diff changeset
369 One thing to avoid is being an \name{open relay}. Open relays allow to relay mail from everywhere to everywhere. This is a major source of spam. The solution is restricting relay\footnote{Relaying is passing mail, that is not from and not for the own system, through it.} access.
204683bfb4e7 wrote much about modules of an MTA
meillo@marmaro.de
parents: 167
diff changeset
370
204683bfb4e7 wrote much about modules of an MTA
meillo@marmaro.de
parents: 167
diff changeset
371 Several ways to restrict access are available. The most simple one is restrictiction by the \NAME{IP} address. No extra complexity is added this way, but static \NAME{IP} addresses are mandatory. This kind of restriction may be enabled using the operating system's \path{hosts.allow} and \path{hosts.deny} files. To allow only connections to port 25 from localhost or the local network \texttt{192.168.100.0/24} insert the line ``\texttt{25: ALL}'' into \path{hosts.deny} and ``\texttt{25: 127.0.0.1, 192.168.100.}'' into \path{hosts.allow}.
163
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
372
170
204683bfb4e7 wrote much about modules of an MTA
meillo@marmaro.de
parents: 167
diff changeset
373 If static access restriction is not possible, for example if mail from locations with changing \NAME{IP} addresses wants to be accepted, some kind of authentication mechanism is required. Three common kinds exist:
204683bfb4e7 wrote much about modules of an MTA
meillo@marmaro.de
parents: 167
diff changeset
374 \begin{enumerate}
185
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
375 \item \SMTP-after-\NAME{POP}: uses authenication on the \NAME{POP} protocol to permit incoming \SMTP\ connections for a limited time afterwards.
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
376 \item \SMTP authentication: is an extension to \SMTP. Authentication can be requested before mail is accepted.
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
377 \item Certificates: confirm the identity of someone.
170
204683bfb4e7 wrote much about modules of an MTA
meillo@marmaro.de
parents: 167
diff changeset
378 \end{enumerate}
204683bfb4e7 wrote much about modules of an MTA
meillo@marmaro.de
parents: 167
diff changeset
379
204683bfb4e7 wrote much about modules of an MTA
meillo@marmaro.de
parents: 167
diff changeset
380
163
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
381
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
382 \subsubsection*{Encryption}
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
383
172
5c873e6478ef wrote about encryption
meillo@marmaro.de
parents: 170
diff changeset
384 Electronic mail is very weak to sniffing attacks, because all data transfer is unencrypted. This concerns the message's content, as well as the email addresses in header and envelope, but also authentication dialogs that may transfer plain text passwords (\NAME{PLAIN} and \NAME{LOGIN} are examples). Adding encryption is therefor wanted.
5c873e6478ef wrote about encryption
meillo@marmaro.de
parents: 170
diff changeset
385
5c873e6478ef wrote about encryption
meillo@marmaro.de
parents: 170
diff changeset
386 The common way to encrypt \SMTP\ dialogs is using \name{Transport Layer Security} (short: \TLS, successor of \NAME{SSL}). \TLS\ encrypts the datagrams of the \name{transport layer}. This means it works below the application protocols and can be used by any of them\citeweb{wikipedia:tls}.
5c873e6478ef wrote about encryption
meillo@marmaro.de
parents: 170
diff changeset
387
5c873e6478ef wrote about encryption
meillo@marmaro.de
parents: 170
diff changeset
388 \TLS\ allows to create secure tunnels through which arbitrary programs can communicate. Hence one can add secure communication afterwards to programs without changing them. \name{OpenSSL} for example---a free implementation---allows traffic to be piped into a command; a secure tunnel is created and the traffic is forwarded through it. Or a secure tunnel can be set up between a local and a remote port; this tunnel can then be used by any application.
5c873e6478ef wrote about encryption
meillo@marmaro.de
parents: 170
diff changeset
389
5c873e6478ef wrote about encryption
meillo@marmaro.de
parents: 170
diff changeset
390 The \NAME{POP} protocol, for example, is good suited for such tunneling, but \SMTP\ is is not generally. Outgoing \SMTP\ client connections can be tunneled without problem---\masqmail\ already provides a configure option called \texttt{wrapper} to do so. Tunneling incomming connections to a server leads to problems with \SMTP. As data comes encrypted through the tunnel to the receiving host and gets then decrypted and forwarded on local to the port the application listens on. From the \MTA's view, this makes all connections appear to come from localhost, unfortunately. Figure \ref{fig:stunnel} depicts the data flow.
5c873e6478ef wrote about encryption
meillo@marmaro.de
parents: 170
diff changeset
391
5c873e6478ef wrote about encryption
meillo@marmaro.de
parents: 170
diff changeset
392 For incoming connections, \NAME{STARTTLS}---defined in \RFC2487---is what \mta{}s implement.
5c873e6478ef wrote about encryption
meillo@marmaro.de
parents: 170
diff changeset
393
5c873e6478ef wrote about encryption
meillo@marmaro.de
parents: 170
diff changeset
394 \masqmail\ is already able to encrypt outgoing connections, but encryption of incoming connections, using \NAME{STARTTLS} should be implemented. This only affects the \SMTP\ server module.
5c873e6478ef wrote about encryption
meillo@marmaro.de
parents: 170
diff changeset
395
165
a7fd6d974d3c added lots of notes about spam, malware, auth, ...
meillo@marmaro.de
parents: 163
diff changeset
396
a7fd6d974d3c added lots of notes about spam, malware, auth, ...
meillo@marmaro.de
parents: 163
diff changeset
397
a7fd6d974d3c added lots of notes about spam, malware, auth, ...
meillo@marmaro.de
parents: 163
diff changeset
398
163
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
399
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
400 \subsubsection*{Spam prevention}
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
401
177
7781ad0811f7 new sections, moved content, and more
meillo@marmaro.de
parents: 173
diff changeset
402 ---
7781ad0811f7 new sections, moved content, and more
meillo@marmaro.de
parents: 173
diff changeset
403 Spam is a major threat nowadays and the goal is to reduce it to a bearable level (see section \ref{sec:swot-analysis}). Spam fighting is a war are where the good guys tend to lose. Putting too much effort there will result in few gain. Real success will only be possible with new---better---protocols and abandonning the weak legacy technologies. Hence \masqmail\ should be able to provide state-of-the-art spam protection, but not more.
7781ad0811f7 new sections, moved content, and more
meillo@marmaro.de
parents: 173
diff changeset
404 ---
7781ad0811f7 new sections, moved content, and more
meillo@marmaro.de
parents: 173
diff changeset
405
173
c51f1be54224 wrote about spam prevention and malware checking
meillo@marmaro.de
parents: 172
diff changeset
406 Spam is a major threat to email, as described in section \ref{sec:swot-analysis}. The two main problems are forgable sender addresses and that it is cheap to send hundreds of thousands of messages. Hence, spam senders can operate in disguise and have minimal cost.
163
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
407
173
c51f1be54224 wrote about spam prevention and malware checking
meillo@marmaro.de
parents: 172
diff changeset
408 As spam is not just a nuisance for end users, but also for the infrastructure---the \mta{}s---by increasing the amount of mail messages, \MTA{}s need to protect themself. Two approaches are used.
c51f1be54224 wrote about spam prevention and malware checking
meillo@marmaro.de
parents: 172
diff changeset
409
177
7781ad0811f7 new sections, moved content, and more
meillo@marmaro.de
parents: 173
diff changeset
410 First refusing spam during the \SMTP\ dialog. This is the way it was meant by the designers of the \SMTP\ protocol. They thought checking the sender and reciptient mail addresses would be enough, but as they are forgable it is not. More and more complex checks need to be done. Checking needs time, but \SMTP\ dialogs time out if it takes too long. Thus only limited time can be used, during the \SMTP\ dialog, for checking if a message seems to be spam. The advantage is that acceptance of bad messages can be simply refused---no responsibility for the message is takes and no further system load is added. See \RFC2505 (especially section 1.5) for detail.
165
a7fd6d974d3c added lots of notes about spam, malware, auth, ...
meillo@marmaro.de
parents: 163
diff changeset
411
173
c51f1be54224 wrote about spam prevention and malware checking
meillo@marmaro.de
parents: 172
diff changeset
412 Second checking for spam after the mail was accepted and queued. Here more processing time can be invested, so more detailed checks can be done. But, as responsibility for messages was taken by accepting them, it is no choice to simply delete spam mail. Checks for spam do not lead to sure results, they just indicate the possibility the message is unwanted mail. \person{Eisentraut} indicates actions to take after a message is recognized as probably spam \cite[pages 18--20]{eisentraut05}. The only acceptable one, for mail the \MTA\ is responsible for, is adding further or rewriting existent header lines. Thus all further work on the message is the same as for non-spam messages.
165
a7fd6d974d3c added lots of notes about spam, malware, auth, ...
meillo@marmaro.de
parents: 163
diff changeset
413
173
c51f1be54224 wrote about spam prevention and malware checking
meillo@marmaro.de
parents: 172
diff changeset
414 Modern \MTA{}s use both techniques in combination. Checks during the \SMTP\ dialog tend to be implemented in the \mta\ to make it fast; checks after the message was queued are often done using external programs (\name{spamassassin} is a well known one). \person{Eisentraut} sees the checks during the \SMTP\ dialog to be essentiell: ``Ganz ohne Analyse während der SMTP-Phase kommt sowieso kein MTA aus, und es ist eine Frage der Einschätzung, wie weit man diese Phase belasten möchte.''\cite[page 25]{eisentraut05} (translated: ``No \MTA\ can go without analysis during the \SMTP\ dialog, anyway, and it is a question of estimation how much to stress this period.'')
163
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
415
173
c51f1be54224 wrote about spam prevention and malware checking
meillo@marmaro.de
parents: 172
diff changeset
416 \NAME{DNS} blacklists (short: \NAME{DNSBL}) and \name{greylisting} are checks to be done before accepting the message. Invoking \name{spamassassin}, to add headers containing the estimated spam probability, is best to be invoked after the message is queued.
165
a7fd6d974d3c added lots of notes about spam, malware, auth, ...
meillo@marmaro.de
parents: 163
diff changeset
417
a7fd6d974d3c added lots of notes about spam, malware, auth, ...
meillo@marmaro.de
parents: 163
diff changeset
418
a7fd6d974d3c added lots of notes about spam, malware, auth, ...
meillo@marmaro.de
parents: 163
diff changeset
419
a7fd6d974d3c added lots of notes about spam, malware, auth, ...
meillo@marmaro.de
parents: 163
diff changeset
420
163
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
421 \subsubsection*{Virus checking}
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
422
173
c51f1be54224 wrote about spam prevention and malware checking
meillo@marmaro.de
parents: 172
diff changeset
423 Related to spam is malicous content (short: \name{malware}) like viruses, worms, trojan horses. They, in contrast to spam, do not affect the \MTA\ itself, as they are in the mail body. The same situation in the real world is post offices opening letters to check if they contain something that could harm the recipient. This is not a mail transport concern. Apart of not being the right program to do the job, the \MTA\---the one which is responsible for the recipient---is at a good position to do this work.
163
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
424
177
7781ad0811f7 new sections, moved content, and more
meillo@marmaro.de
parents: 173
diff changeset
425 In any way should malware checking be done by external programs that may be invoked by the \mta. But using mail deliver and processing agents, like \name{procmail}, seem to be better suited locations to invoke content scanners.
161
18b7b517e2dd wrote about discussion on architecture
meillo@marmaro.de
parents: 155
diff changeset
426
177
7781ad0811f7 new sections, moved content, and more
meillo@marmaro.de
parents: 173
diff changeset
427 A popular email filter framework is \name{amavis} which integrates various spam and virus scanners. The common setup includes a receiving \MTA\ which sends it to \name{amavis} using \SMTP, \name{amavis} processes the mail and sends it then to a second \MTA\ that does the outgoing transfer. \postfix\ and \exim\ can be configured so that one instance can work as both, the \MTA\ for incoming and outgoing transfer. A setup with \sendmail\ needs two separate instances running. It must be quarateed that all mail flows through the scanner.
7781ad0811f7 new sections, moved content, and more
meillo@marmaro.de
parents: 173
diff changeset
428
7781ad0811f7 new sections, moved content, and more
meillo@marmaro.de
parents: 173
diff changeset
429 A future \masqmail\ would do good to have a single point, where all traffic flows through, that is able to invoke external programs to do mail processing of any kind.
161
18b7b517e2dd wrote about discussion on architecture
meillo@marmaro.de
parents: 155
diff changeset
430
165
a7fd6d974d3c added lots of notes about spam, malware, auth, ...
meillo@marmaro.de
parents: 163
diff changeset
431
177
7781ad0811f7 new sections, moved content, and more
meillo@marmaro.de
parents: 173
diff changeset
432 %AMaViS (amavisd-new): email filter framework to integrate spam and virus scanner
7781ad0811f7 new sections, moved content, and more
meillo@marmaro.de
parents: 173
diff changeset
433 %\begin{verbatim}
7781ad0811f7 new sections, moved content, and more
meillo@marmaro.de
parents: 173
diff changeset
434 %internet -->25 MTA -->10024 amavis -->10025 MTA --> reciptient
7781ad0811f7 new sections, moved content, and more
meillo@marmaro.de
parents: 173
diff changeset
435 %| |
7781ad0811f7 new sections, moved content, and more
meillo@marmaro.de
parents: 173
diff changeset
436 %+----------------------------+
7781ad0811f7 new sections, moved content, and more
meillo@marmaro.de
parents: 173
diff changeset
437 %\end{verbatim}
7781ad0811f7 new sections, moved content, and more
meillo@marmaro.de
parents: 173
diff changeset
438 %
7781ad0811f7 new sections, moved content, and more
meillo@marmaro.de
parents: 173
diff changeset
439 %postfix and exim can habe both mta servises in the same instance, sendmail needs two instances running.
7781ad0811f7 new sections, moved content, and more
meillo@marmaro.de
parents: 173
diff changeset
440 %
7781ad0811f7 new sections, moved content, and more
meillo@marmaro.de
parents: 173
diff changeset
441 %MailScanner:
7781ad0811f7 new sections, moved content, and more
meillo@marmaro.de
parents: 173
diff changeset
442 %incoming queue --> MailScanner --> outgoing queue
7781ad0811f7 new sections, moved content, and more
meillo@marmaro.de
parents: 173
diff changeset
443 %
7781ad0811f7 new sections, moved content, and more
meillo@marmaro.de
parents: 173
diff changeset
444 %postfix: with one instance possible, exim and sendmail need two instances running
165
a7fd6d974d3c added lots of notes about spam, malware, auth, ...
meillo@marmaro.de
parents: 163
diff changeset
445
161
18b7b517e2dd wrote about discussion on architecture
meillo@marmaro.de
parents: 155
diff changeset
446
173
c51f1be54224 wrote about spam prevention and malware checking
meillo@marmaro.de
parents: 172
diff changeset
447 %message body <-> envelope, header
c51f1be54224 wrote about spam prevention and malware checking
meillo@marmaro.de
parents: 172
diff changeset
448 %
c51f1be54224 wrote about spam prevention and malware checking
meillo@marmaro.de
parents: 172
diff changeset
449 %anti-virus: clamav
c51f1be54224 wrote about spam prevention and malware checking
meillo@marmaro.de
parents: 172
diff changeset
450 %postfix: via amavis
c51f1be54224 wrote about spam prevention and malware checking
meillo@marmaro.de
parents: 172
diff changeset
451 %exim: via content-scanning-feature called from acl
c51f1be54224 wrote about spam prevention and malware checking
meillo@marmaro.de
parents: 172
diff changeset
452 %sendmail: with milter
c51f1be54224 wrote about spam prevention and malware checking
meillo@marmaro.de
parents: 172
diff changeset
453 %procmail
c51f1be54224 wrote about spam prevention and malware checking
meillo@marmaro.de
parents: 172
diff changeset
454 %
c51f1be54224 wrote about spam prevention and malware checking
meillo@marmaro.de
parents: 172
diff changeset
455 %virus scanner work on file level
c51f1be54224 wrote about spam prevention and malware checking
meillo@marmaro.de
parents: 172
diff changeset
456 %amavis receives mail via smtp or pipe, splits it in its parts (MIME) and extracks archives, the come the virus scanners
c51f1be54224 wrote about spam prevention and malware checking
meillo@marmaro.de
parents: 172
diff changeset
457 %if the mail is okay, it goes via smtp to a second mta
c51f1be54224 wrote about spam prevention and malware checking
meillo@marmaro.de
parents: 172
diff changeset
458
c51f1be54224 wrote about spam prevention and malware checking
meillo@marmaro.de
parents: 172
diff changeset
459 %what amavis recognizes:
c51f1be54224 wrote about spam prevention and malware checking
meillo@marmaro.de
parents: 172
diff changeset
460 %- invalid headers
c51f1be54224 wrote about spam prevention and malware checking
meillo@marmaro.de
parents: 172
diff changeset
461 %- banned files
c51f1be54224 wrote about spam prevention and malware checking
meillo@marmaro.de
parents: 172
diff changeset
462 %- viruses
c51f1be54224 wrote about spam prevention and malware checking
meillo@marmaro.de
parents: 172
diff changeset
463 %- spam (using spam assassin)
c51f1be54224 wrote about spam prevention and malware checking
meillo@marmaro.de
parents: 172
diff changeset
464 %
c51f1be54224 wrote about spam prevention and malware checking
meillo@marmaro.de
parents: 172
diff changeset
465 %mimedefang: uses milter interface with sendmail
c51f1be54224 wrote about spam prevention and malware checking
meillo@marmaro.de
parents: 172
diff changeset
466
161
18b7b517e2dd wrote about discussion on architecture
meillo@marmaro.de
parents: 155
diff changeset
467
18b7b517e2dd wrote about discussion on architecture
meillo@marmaro.de
parents: 155
diff changeset
468
163
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
469 \subsubsection*{Archiving}
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
470
177
7781ad0811f7 new sections, moved content, and more
meillo@marmaro.de
parents: 173
diff changeset
471 Mail archiving and auditability become more important as electronic mail becomes more important. Ability to archive verbatim copies of every mail coming into and every mail going out of the system, with relation between them, appears to be a goal to achieve.
146
2c4673d983c3 wrote about requirements (related to directions to go)
meillo@marmaro.de
parents: 142
diff changeset
472
177
7781ad0811f7 new sections, moved content, and more
meillo@marmaro.de
parents: 173
diff changeset
473 \postfix\ for example has a \texttt{always\_bcc} feature, to send a copy of every mail to a definable reciptient. At least this funtionality should be given, although a more complete approach is preferable.
161
18b7b517e2dd wrote about discussion on architecture
meillo@marmaro.de
parents: 155
diff changeset
474
18b7b517e2dd wrote about discussion on architecture
meillo@marmaro.de
parents: 155
diff changeset
475
18b7b517e2dd wrote about discussion on architecture
meillo@marmaro.de
parents: 155
diff changeset
476
18b7b517e2dd wrote about discussion on architecture
meillo@marmaro.de
parents: 155
diff changeset
477
177
7781ad0811f7 new sections, moved content, and more
meillo@marmaro.de
parents: 173
diff changeset
478
185
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
479 \subsection{The resulting architecture}
177
7781ad0811f7 new sections, moved content, and more
meillo@marmaro.de
parents: 173
diff changeset
480
178
b426a663d5f0 wrote about modules and queues
meillo@marmaro.de
parents: 177
diff changeset
481 The result is a symetric design, featuring the following parts: Any number of handlers for incoming connections to receive mail and pass it to the module that stores it into the incoming queue. A central scanning module take mail from the incoming queue, processes it in various ways and puts it afterwards into the outgoing queue. Another module takes it out there and passes it to a matching transport module that transfers it to the destination. In other words, three main modules (queue-in, scanning, queue-out) are connected by the two queues (incoming, outgoing); on each end are more modules to receive and send mail---for each protocol one. Figure \ref{fig:masqmail-arch-new} depicts the new designed architecture.
177
7781ad0811f7 new sections, moved content, and more
meillo@marmaro.de
parents: 173
diff changeset
482
7781ad0811f7 new sections, moved content, and more
meillo@marmaro.de
parents: 173
diff changeset
483 \begin{figure}
7781ad0811f7 new sections, moved content, and more
meillo@marmaro.de
parents: 173
diff changeset
484 \begin{center}
7781ad0811f7 new sections, moved content, and more
meillo@marmaro.de
parents: 173
diff changeset
485 \input{input/masqmail-arch-new.tex}
7781ad0811f7 new sections, moved content, and more
meillo@marmaro.de
parents: 173
diff changeset
486 \end{center}
7781ad0811f7 new sections, moved content, and more
meillo@marmaro.de
parents: 173
diff changeset
487 \caption{A new designed architecture for \masqmail}
7781ad0811f7 new sections, moved content, and more
meillo@marmaro.de
parents: 173
diff changeset
488 \label{fig:masqmail-arch-new}
7781ad0811f7 new sections, moved content, and more
meillo@marmaro.de
parents: 173
diff changeset
489 \end{figure}
161
18b7b517e2dd wrote about discussion on architecture
meillo@marmaro.de
parents: 155
diff changeset
490
178
b426a663d5f0 wrote about modules and queues
meillo@marmaro.de
parents: 177
diff changeset
491 This architecture is heavily influenced by the ones of \qmail\ and \postfix. Both have different incoming channels that merge in the module that puts mail into the queue; central is the queue (or more of them); and one module takes mail from the queue and passes it to one of the outgoing channels. Mail processing, in any way, is build in in a more explicit way than done in the other two. It is more similar to the \NAME{AR} module of \name{sendmail X}, which is the central point for spam checking.
b426a663d5f0 wrote about modules and queues
meillo@marmaro.de
parents: 177
diff changeset
492
b426a663d5f0 wrote about modules and queues
meillo@marmaro.de
parents: 177
diff changeset
493 Special regard was put on addable support for further mail transfer protocols. This appears to be most similar to \qmail, which was designed to handle multiple protocols.
b426a663d5f0 wrote about modules and queues
meillo@marmaro.de
parents: 177
diff changeset
494 %fixme: do i need all this ``quesses''??
161
18b7b517e2dd wrote about discussion on architecture
meillo@marmaro.de
parents: 155
diff changeset
495
149
ccf0de1ae337 new content and rework
meillo@marmaro.de
parents: 146
diff changeset
496
185
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
497 \subsubsection*{Modules and queues}
177
7781ad0811f7 new sections, moved content, and more
meillo@marmaro.de
parents: 173
diff changeset
498
178
b426a663d5f0 wrote about modules and queues
meillo@marmaro.de
parents: 177
diff changeset
499 The new architecture consists of several modules and two queues. They are defined in more detail now, and the jobs, identified above, are assigned to them. First the three main modules, then the queues, and afterwards the modules for incoming and outgoing transfer.
b426a663d5f0 wrote about modules and queues
meillo@marmaro.de
parents: 177
diff changeset
500
b426a663d5f0 wrote about modules and queues
meillo@marmaro.de
parents: 177
diff changeset
501
b426a663d5f0 wrote about modules and queues
meillo@marmaro.de
parents: 177
diff changeset
502 The \name{queue-in} module creates new spool files in the \name{incoming} queue for incoming messages. It is a process running in background, waiting for connections from one of the receiver modules. When one of them requests for a new spool file, the \name{queue-in} module opens one and returns a positive result. The receiver module then sends the envelope and message, which is written into the spool file by \name{queue-in}. If all went well, another positive result is returend.
182
e35c7962d84f wrote about spool file and permissions
meillo@marmaro.de
parents: 180
diff changeset
503 %fixme: should be no daemon
178
b426a663d5f0 wrote about modules and queues
meillo@marmaro.de
parents: 177
diff changeset
504
b426a663d5f0 wrote about modules and queues
meillo@marmaro.de
parents: 177
diff changeset
505
b426a663d5f0 wrote about modules and queues
meillo@marmaro.de
parents: 177
diff changeset
506 The \name{scanning} module is the central part of the system. It takes spooled messages from the \name{incoming} queue, works on them, and writes them to the \name{outgoing} queue afterwards (the message is then removed from the \name{incoming} queue, of course). The main job is the processing done on the message. Headers are fixed and missing ones are added if necessary, aliasing is done, and external processing of any kind is triggered. The \name{scanning} module can run in background and look for new mail in regular intvals or signals may be sent to it by \name{queue-in}. Alternatively it can be called by \name{cron}, for example, to do single runs.
b426a663d5f0 wrote about modules and queues
meillo@marmaro.de
parents: 177
diff changeset
507
b426a663d5f0 wrote about modules and queues
meillo@marmaro.de
parents: 177
diff changeset
508
b426a663d5f0 wrote about modules and queues
meillo@marmaro.de
parents: 177
diff changeset
509 The \name{queue-out} module takes messages from the \name{outgoing} queue, queries information about the online connection, and then selects matching routes, creates envelopes for each recipient and passes the messages to the correct transport module. Successfully transfered messages are removed from the \name{outgoing} queue. This module includes some tasks specific to \masqmail.
177
7781ad0811f7 new sections, moved content, and more
meillo@marmaro.de
parents: 173
diff changeset
510
178
b426a663d5f0 wrote about modules and queues
meillo@marmaro.de
parents: 177
diff changeset
511
b426a663d5f0 wrote about modules and queues
meillo@marmaro.de
parents: 177
diff changeset
512 The \name{incoming} queue stores messages received via one of the incoming channels. The messages are in unprocessed form; only envelope data is prepended.
b426a663d5f0 wrote about modules and queues
meillo@marmaro.de
parents: 177
diff changeset
513
177
7781ad0811f7 new sections, moved content, and more
meillo@marmaro.de
parents: 173
diff changeset
514
178
b426a663d5f0 wrote about modules and queues
meillo@marmaro.de
parents: 177
diff changeset
515 The \name{outgoing} queue contains processed messages. The header and envelope information is complete and in valid form.
b426a663d5f0 wrote about modules and queues
meillo@marmaro.de
parents: 177
diff changeset
516
b426a663d5f0 wrote about modules and queues
meillo@marmaro.de
parents: 177
diff changeset
517 \name{Receiver modules} are the communication interface between outside senders and the \name{queue-in} module. Each protocol needs a corresponding \name{receiver module} to be supported. Most popular are the \name{sendmail} module (which is a command to be called from the local host) and the \name{smtpd} module (which listens on port 25). Other modules to support other protocols may be added as needed.
b426a663d5f0 wrote about modules and queues
meillo@marmaro.de
parents: 177
diff changeset
518
b426a663d5f0 wrote about modules and queues
meillo@marmaro.de
parents: 177
diff changeset
519 \name{Transport modules}, on the oppersite side of the system, are the modules to send outgoing mail; they are the interface between \name{queue-out} and remote hosts or local commands for further processing. The most popular ones are the \name{smtp} module (which acts as the \SMTP\ client) and the \name{pipe} module (to interface gateways to other systems or networks, like fax or uucp). A module for local delivery is not included, as it is in most other \MTA{}s; the reasons are described in FIXME.%fixme
b426a663d5f0 wrote about modules and queues
meillo@marmaro.de
parents: 177
diff changeset
520 Thus a \name{mail delivery agent} (like \name{procmail}) is to be used with the \name{pipe} module.
93
a6f8a93abd64 new chapter 4 (split ch5); added lots of annotations
meillo@marmaro.de
parents:
diff changeset
521
132
a83a29e10b10 new books
meillo@marmaro.de
parents: 129
diff changeset
522
93
a6f8a93abd64 new chapter 4 (split ch5); added lots of annotations
meillo@marmaro.de
parents:
diff changeset
523
185
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
524 \subsubsection*{Inter-module communication}
180
d75bd7a72d8b wrote about IPC, drawed picture of new arch
meillo@marmaro.de
parents: 178
diff changeset
525
d75bd7a72d8b wrote about IPC, drawed picture of new arch
meillo@marmaro.de
parents: 178
diff changeset
526 Communication between modules is required to exchange data and status information. It is also called ``Inter-process communication'' (short: \NAME{IPC}), as modules are programs being part of a larger system, and processes are generally seen as programs in execution.
d75bd7a72d8b wrote about IPC, drawed picture of new arch
meillo@marmaro.de
parents: 178
diff changeset
527
d75bd7a72d8b wrote about IPC, drawed picture of new arch
meillo@marmaro.de
parents: 178
diff changeset
528 The connections between \name{queue-in} and \name{scanning}, aswell as between \name{scanning} and \name{queue-out} is provided by the queues, only sending signals to trigger instant runs may be useful. Communication between receiving and transport modules and the outside world are done using the specific protocol they do handle.
d75bd7a72d8b wrote about IPC, drawed picture of new arch
meillo@marmaro.de
parents: 178
diff changeset
529
d75bd7a72d8b wrote about IPC, drawed picture of new arch
meillo@marmaro.de
parents: 178
diff changeset
530 Left is only communication between the receiver modules and \name{queue-in}, and between \name{queue-out} and the transport modules. Data is exchanged done using \unix\ pipes and a simple protocol is used.
d75bd7a72d8b wrote about IPC, drawed picture of new arch
meillo@marmaro.de
parents: 178
diff changeset
531
d75bd7a72d8b wrote about IPC, drawed picture of new arch
meillo@marmaro.de
parents: 178
diff changeset
532 \begin{figure}
d75bd7a72d8b wrote about IPC, drawed picture of new arch
meillo@marmaro.de
parents: 178
diff changeset
533 \begin{center}
d75bd7a72d8b wrote about IPC, drawed picture of new arch
meillo@marmaro.de
parents: 178
diff changeset
534 \input{input/ipc-protocol.tex}
d75bd7a72d8b wrote about IPC, drawed picture of new arch
meillo@marmaro.de
parents: 178
diff changeset
535 \end{center}
d75bd7a72d8b wrote about IPC, drawed picture of new arch
meillo@marmaro.de
parents: 178
diff changeset
536 \caption{State diagram of the protocol used for \NAME{IPC}}
d75bd7a72d8b wrote about IPC, drawed picture of new arch
meillo@marmaro.de
parents: 178
diff changeset
537 \label{fig:ipc-protocol}
d75bd7a72d8b wrote about IPC, drawed picture of new arch
meillo@marmaro.de
parents: 178
diff changeset
538 \end{figure}
d75bd7a72d8b wrote about IPC, drawed picture of new arch
meillo@marmaro.de
parents: 178
diff changeset
539
d75bd7a72d8b wrote about IPC, drawed picture of new arch
meillo@marmaro.de
parents: 178
diff changeset
540 % timing
d75bd7a72d8b wrote about IPC, drawed picture of new arch
meillo@marmaro.de
parents: 178
diff changeset
541 One dialog consists of the four phases: connection attempt, acceptance reply, data transfer, success reply. The order is always the same. The connection attempt and data transfer are sent by the client process; replies are sent by the server process.
182
e35c7962d84f wrote about spool file and permissions
meillo@marmaro.de
parents: 180
diff changeset
542 %fixme: split between header and data
180
d75bd7a72d8b wrote about IPC, drawed picture of new arch
meillo@marmaro.de
parents: 178
diff changeset
543
d75bd7a72d8b wrote about IPC, drawed picture of new arch
meillo@marmaro.de
parents: 178
diff changeset
544 % semantics
d75bd7a72d8b wrote about IPC, drawed picture of new arch
meillo@marmaro.de
parents: 178
diff changeset
545 The connection attempt is simply opening the connection. This starts the dialog. A positive reply by the server leads to the data transfer, but a negative reply refuses the connection and resets both client and server to the state before the connection attempt. If the connection attempt was accepted, the client sends the data ending with a terminator sequence. When this terminator appears, the server process knows the complete data was transfered. The server process takes responsibility of the data in sending a positive success reply. A negative success reply resets both client and server to the state before the connection attempt.
d75bd7a72d8b wrote about IPC, drawed picture of new arch
meillo@marmaro.de
parents: 178
diff changeset
546
d75bd7a72d8b wrote about IPC, drawed picture of new arch
meillo@marmaro.de
parents: 178
diff changeset
547 The data transfered needs to be of specific format. Used is the same format in which messages are spooled in the mail queues. See the following section for details. %fixme: check if it is the following section
182
e35c7962d84f wrote about spool file and permissions
meillo@marmaro.de
parents: 180
diff changeset
548 %fixme: split between header and data
180
d75bd7a72d8b wrote about IPC, drawed picture of new arch
meillo@marmaro.de
parents: 178
diff changeset
549
d75bd7a72d8b wrote about IPC, drawed picture of new arch
meillo@marmaro.de
parents: 178
diff changeset
550 % syntax
d75bd7a72d8b wrote about IPC, drawed picture of new arch
meillo@marmaro.de
parents: 178
diff changeset
551 Data transfer is done sending plain text data. %fixme: utf8 ?
182
e35c7962d84f wrote about spool file and permissions
meillo@marmaro.de
parents: 180
diff changeset
552 The terminator sequence used to indicate the end of the data transfer is a single dot on a line on its own. Line separators are the combination of \name{Carriage Return} and \name{Line Feed}, as it is used in various Internet protocols like \SMTP. Replys are one-digit numbers with \texttt{0} meaning success and any other number (\texttt{1}--\texttt{9}) indicate failure. %fixme: What are the octal values?
e35c7962d84f wrote about spool file and permissions
meillo@marmaro.de
parents: 180
diff changeset
553 %fixme: split between header and data
180
d75bd7a72d8b wrote about IPC, drawed picture of new arch
meillo@marmaro.de
parents: 178
diff changeset
554
d75bd7a72d8b wrote about IPC, drawed picture of new arch
meillo@marmaro.de
parents: 178
diff changeset
555 Figure \ref{fig:ipc-protocol} is a state diagram for the protocol.
177
7781ad0811f7 new sections, moved content, and more
meillo@marmaro.de
parents: 173
diff changeset
556
93
a6f8a93abd64 new chapter 4 (split ch5); added lots of annotations
meillo@marmaro.de
parents:
diff changeset
557
a6f8a93abd64 new chapter 4 (split ch5); added lots of annotations
meillo@marmaro.de
parents:
diff changeset
558
185
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
559 \subsubsection*{Spool file format}
177
7781ad0811f7 new sections, moved content, and more
meillo@marmaro.de
parents: 173
diff changeset
560
182
e35c7962d84f wrote about spool file and permissions
meillo@marmaro.de
parents: 180
diff changeset
561 The spool file format is basically the same as the one in current \masqmail: one file for the message body, the other for envelope and header information. The data file is stored in a separate data pool. It is written by \name{queue-in}, \name{scanning} can read it if necessary, \name{queue-out} reads it to generate the outgoing message, and deletes it after successful transfer. The header file (including the envelope) is written into the \name{incoming} queue. The \name{scanning} modules reads it, processes it, and writes a modified copy into the \name{outgoing} queue; the file in \name{incoming} is deleted then. \name{queue-out} finally takes the header file from \name{outgoing} to generate the resulting message. This data flow is shown in figure \ref{fig:queue-data-flow}.
e35c7962d84f wrote about spool file and permissions
meillo@marmaro.de
parents: 180
diff changeset
562
e35c7962d84f wrote about spool file and permissions
meillo@marmaro.de
parents: 180
diff changeset
563 \begin{figure}
e35c7962d84f wrote about spool file and permissions
meillo@marmaro.de
parents: 180
diff changeset
564 \begin{center}
e35c7962d84f wrote about spool file and permissions
meillo@marmaro.de
parents: 180
diff changeset
565 \input{input/queue-data-flow.tex}
e35c7962d84f wrote about spool file and permissions
meillo@marmaro.de
parents: 180
diff changeset
566 \end{center}
e35c7962d84f wrote about spool file and permissions
meillo@marmaro.de
parents: 180
diff changeset
567 \caption{Data flow of messages in the queue}
e35c7962d84f wrote about spool file and permissions
meillo@marmaro.de
parents: 180
diff changeset
568 \label{fig:queue-data-flow}
e35c7962d84f wrote about spool file and permissions
meillo@marmaro.de
parents: 180
diff changeset
569 \end{figure}
e35c7962d84f wrote about spool file and permissions
meillo@marmaro.de
parents: 180
diff changeset
570
e35c7962d84f wrote about spool file and permissions
meillo@marmaro.de
parents: 180
diff changeset
571 The queue consists of three directories within the queue path. Two, named \name{incoming} and \name{outgoing}, for storing the header files; one, called \name{pool}, to store the message bodies. The files being part of one message share the same unique name. The header files internal structure can be the same as the one of current \masqmail.
e35c7962d84f wrote about spool file and permissions
meillo@marmaro.de
parents: 180
diff changeset
572
e35c7962d84f wrote about spool file and permissions
meillo@marmaro.de
parents: 180
diff changeset
573 Messages in queues are a header file in \name{incoming} or \name{outgoing} and a data file in \name{pool}. The header file owner's executable bit indicates if the file is ready for further processing: the module that writes the file into the queue sets the bit as last action. Modules that read from the queue can process messages with the bit set.
180
d75bd7a72d8b wrote about IPC, drawed picture of new arch
meillo@marmaro.de
parents: 178
diff changeset
574
182
e35c7962d84f wrote about spool file and permissions
meillo@marmaro.de
parents: 180
diff changeset
575 No spool files are modified after they are written to disk. Modifications to header files can be made by the \name{scanning} module in the ``move'' from \name{incoming} to \name{outgoing}---it is a create and remove, actually. Further rewriting can happen in \name{queue-out}, as well without altering the file.
e35c7962d84f wrote about spool file and permissions
meillo@marmaro.de
parents: 180
diff changeset
576
e35c7962d84f wrote about spool file and permissions
meillo@marmaro.de
parents: 180
diff changeset
577 Data files do not change at all within the system. They are written in default local plain text format. Required translation is done in the receiver and transport modules.
e35c7962d84f wrote about spool file and permissions
meillo@marmaro.de
parents: 180
diff changeset
578
180
d75bd7a72d8b wrote about IPC, drawed picture of new arch
meillo@marmaro.de
parents: 178
diff changeset
579
185
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
580 \begin{tabular}[hbt]{ l l }
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
581
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
582 \mbox{ queue-in:} & \mbox{
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
583 \begin{tabular}[hbt]{| c | c | c |}
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
584 \hline
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
585 incoming & outgoing & pool \\
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
586 \hline
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
587 \hline
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
588 - & - & - \\
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
589 \hline
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
590 0600 & - & - \\
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
591 \hline
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
592 0600 & - & 0600 \\
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
593 \hline
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
594 0700 & - & 0600 \\
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
595 \hline
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
596 \end{tabular}
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
597 } \\
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
598
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
599 \quad & \\
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
600
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
601 \mbox{scanning:} & \mbox{
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
602 \begin{tabular}[hbt]{| c | c | c |}
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
603 \hline
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
604 incoming & outgoing & pool \\
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
605 \hline
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
606 \hline
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
607 0700 & - & 0600 \\
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
608 \hline
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
609 0700 & 0600 & 0600 \\
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
610 \hline
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
611 0700 & 0700 & 0600 \\
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
612 \hline
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
613 - & 0700 & 0600 \\
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
614 \hline
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
615 \end{tabular}
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
616 } \\
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
617
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
618 \quad & \\
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
619
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
620 \mbox{queue-out:} & \mbox{
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
621 \begin{tabular}[hbt]{| c | c | c |}
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
622 \hline
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
623 incoming & outgoing & pool \\
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
624 \hline
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
625 \hline
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
626 - & 0700 & 0600 \\
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
627 \hline
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
628 - & 0700 & - \\
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
629 \hline
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
630 - & - & - \\
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
631 \hline
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
632 \end{tabular}
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
633 } \\
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
634
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
635 \end{tabular}
180
d75bd7a72d8b wrote about IPC, drawed picture of new arch
meillo@marmaro.de
parents: 178
diff changeset
636
182
e35c7962d84f wrote about spool file and permissions
meillo@marmaro.de
parents: 180
diff changeset
637 A sample header file.
180
d75bd7a72d8b wrote about IPC, drawed picture of new arch
meillo@marmaro.de
parents: 178
diff changeset
638 \begin{verbatim}
182
e35c7962d84f wrote about spool file and permissions
meillo@marmaro.de
parents: 180
diff changeset
639 1LGtYh-0ut-00 (backup copy of the file name)
e35c7962d84f wrote about spool file and permissions
meillo@marmaro.de
parents: 180
diff changeset
640 MF:<meillo@dream> (envelope: sender)
e35c7962d84f wrote about spool file and permissions
meillo@marmaro.de
parents: 180
diff changeset
641 RT: <user@example.org> (envelope: recipient)
e35c7962d84f wrote about spool file and permissions
meillo@marmaro.de
parents: 180
diff changeset
642 PR:local (meta info: protocol)
e35c7962d84f wrote about spool file and permissions
meillo@marmaro.de
parents: 180
diff changeset
643 ID:meillo (meta info: id/user/ip)
e35c7962d84f wrote about spool file and permissions
meillo@marmaro.de
parents: 180
diff changeset
644 DS: 18 (meta info: size)
e35c7962d84f wrote about spool file and permissions
meillo@marmaro.de
parents: 180
diff changeset
645 TR: 1230462707 (meta info: timestamp)
e35c7962d84f wrote about spool file and permissions
meillo@marmaro.de
parents: 180
diff changeset
646 (following: headers)
e35c7962d84f wrote about spool file and permissions
meillo@marmaro.de
parents: 180
diff changeset
647 HD:Received: from meillo by dream with local (masqmail 0.2.21) id
e35c7962d84f wrote about spool file and permissions
meillo@marmaro.de
parents: 180
diff changeset
648 1LGtYh-0ut-00 for <user@example.org>; Sun, 28 Dec 2008 12:11:47 +0100
e35c7962d84f wrote about spool file and permissions
meillo@marmaro.de
parents: 180
diff changeset
649 HD:To: user@example.org
e35c7962d84f wrote about spool file and permissions
meillo@marmaro.de
parents: 180
diff changeset
650 HD:Subject: test mail
e35c7962d84f wrote about spool file and permissions
meillo@marmaro.de
parents: 180
diff changeset
651 HD:From: <meillo@dream>
e35c7962d84f wrote about spool file and permissions
meillo@marmaro.de
parents: 180
diff changeset
652 HD:Date: Sun, 28 Dec 2008 12:11:47 +0100
e35c7962d84f wrote about spool file and permissions
meillo@marmaro.de
parents: 180
diff changeset
653 HD:Message-ID: <1LGtYh-0ut-00@dream>
180
d75bd7a72d8b wrote about IPC, drawed picture of new arch
meillo@marmaro.de
parents: 178
diff changeset
654 \end{verbatim}
d75bd7a72d8b wrote about IPC, drawed picture of new arch
meillo@marmaro.de
parents: 178
diff changeset
655
d75bd7a72d8b wrote about IPC, drawed picture of new arch
meillo@marmaro.de
parents: 178
diff changeset
656
177
7781ad0811f7 new sections, moved content, and more
meillo@marmaro.de
parents: 173
diff changeset
657
182
e35c7962d84f wrote about spool file and permissions
meillo@marmaro.de
parents: 180
diff changeset
658
185
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
659 \subsubsection*{Rights and permission}
109
de590ff06051 changes suggested by schaeffter
meillo@marmaro.de
parents: 99
diff changeset
660
182
e35c7962d84f wrote about spool file and permissions
meillo@marmaro.de
parents: 180
diff changeset
661 The user set required for \qmail\ seems to be too complex. One special user, like \postfix\ uses, is more appropriate. \name{root} privilege and \name{setuid} permission is avoided as much as possible.
e35c7962d84f wrote about spool file and permissions
meillo@marmaro.de
parents: 180
diff changeset
662
e35c7962d84f wrote about spool file and permissions
meillo@marmaro.de
parents: 180
diff changeset
663 Table \ref{tab:new-masqmail-permissions} shows the suggested ownership and permissions of the modules. Figure \ref{fig:new-masqmail-queue} shows the permissions and ownership used for the queue.
e35c7962d84f wrote about spool file and permissions
meillo@marmaro.de
parents: 180
diff changeset
664
e35c7962d84f wrote about spool file and permissions
meillo@marmaro.de
parents: 180
diff changeset
665 \begin{table}
e35c7962d84f wrote about spool file and permissions
meillo@marmaro.de
parents: 180
diff changeset
666 \begin{center}
e35c7962d84f wrote about spool file and permissions
meillo@marmaro.de
parents: 180
diff changeset
667 \input{input/new-masqmail-permissions.tex}
e35c7962d84f wrote about spool file and permissions
meillo@marmaro.de
parents: 180
diff changeset
668 \end{center}
e35c7962d84f wrote about spool file and permissions
meillo@marmaro.de
parents: 180
diff changeset
669 \caption{Ownership and permissions of the modules}
e35c7962d84f wrote about spool file and permissions
meillo@marmaro.de
parents: 180
diff changeset
670 \label{tab:new-masqmail-permission}
e35c7962d84f wrote about spool file and permissions
meillo@marmaro.de
parents: 180
diff changeset
671 \end{table}
e35c7962d84f wrote about spool file and permissions
meillo@marmaro.de
parents: 180
diff changeset
672
e35c7962d84f wrote about spool file and permissions
meillo@marmaro.de
parents: 180
diff changeset
673 \begin{figure}
e35c7962d84f wrote about spool file and permissions
meillo@marmaro.de
parents: 180
diff changeset
674 \begin{center}
e35c7962d84f wrote about spool file and permissions
meillo@marmaro.de
parents: 180
diff changeset
675 \input{input/new-masqmail-queue.tex}
e35c7962d84f wrote about spool file and permissions
meillo@marmaro.de
parents: 180
diff changeset
676 \end{center}
e35c7962d84f wrote about spool file and permissions
meillo@marmaro.de
parents: 180
diff changeset
677 \caption{Ownership and permissions of the queue}
e35c7962d84f wrote about spool file and permissions
meillo@marmaro.de
parents: 180
diff changeset
678 \label{fig:new-masqmail-queue}
e35c7962d84f wrote about spool file and permissions
meillo@marmaro.de
parents: 180
diff changeset
679 \end{figure}
e35c7962d84f wrote about spool file and permissions
meillo@marmaro.de
parents: 180
diff changeset
680
e35c7962d84f wrote about spool file and permissions
meillo@marmaro.de
parents: 180
diff changeset
681
e35c7962d84f wrote about spool file and permissions
meillo@marmaro.de
parents: 180
diff changeset
682
e35c7962d84f wrote about spool file and permissions
meillo@marmaro.de
parents: 180
diff changeset
683
e35c7962d84f wrote about spool file and permissions
meillo@marmaro.de
parents: 180
diff changeset
684
180
d75bd7a72d8b wrote about IPC, drawed picture of new arch
meillo@marmaro.de
parents: 178
diff changeset
685 setuid/setgid or not?
149
ccf0de1ae337 new content and rework
meillo@marmaro.de
parents: 146
diff changeset
686
180
d75bd7a72d8b wrote about IPC, drawed picture of new arch
meillo@marmaro.de
parents: 178
diff changeset
687 what can crash if an attacker succeeds?
d75bd7a72d8b wrote about IPC, drawed picture of new arch
meillo@marmaro.de
parents: 178
diff changeset
688
d75bd7a72d8b wrote about IPC, drawed picture of new arch
meillo@marmaro.de
parents: 178
diff changeset
689 where to drop privelege?
d75bd7a72d8b wrote about IPC, drawed picture of new arch
meillo@marmaro.de
parents: 178
diff changeset
690
d75bd7a72d8b wrote about IPC, drawed picture of new arch
meillo@marmaro.de
parents: 178
diff changeset
691 how is which process invoked?
d75bd7a72d8b wrote about IPC, drawed picture of new arch
meillo@marmaro.de
parents: 178
diff changeset
692
d75bd7a72d8b wrote about IPC, drawed picture of new arch
meillo@marmaro.de
parents: 178
diff changeset
693 master process? needed, or wanted?
d75bd7a72d8b wrote about IPC, drawed picture of new arch
meillo@marmaro.de
parents: 178
diff changeset
694
d75bd7a72d8b wrote about IPC, drawed picture of new arch
meillo@marmaro.de
parents: 178
diff changeset
695 which are the daemon processes?
149
ccf0de1ae337 new content and rework
meillo@marmaro.de
parents: 146
diff changeset
696
ccf0de1ae337 new content and rework
meillo@marmaro.de
parents: 146
diff changeset
697
163
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
698
149
ccf0de1ae337 new content and rework
meillo@marmaro.de
parents: 146
diff changeset
699
ccf0de1ae337 new content and rework
meillo@marmaro.de
parents: 146
diff changeset
700
93
a6f8a93abd64 new chapter 4 (split ch5); added lots of annotations
meillo@marmaro.de
parents:
diff changeset
701
a6f8a93abd64 new chapter 4 (split ch5); added lots of annotations
meillo@marmaro.de
parents:
diff changeset
702
185
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
703 http://fanf.livejournal.com/50917.html %how not to design an mta - the sendmail command
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
704 http://fanf.livejournal.com/51349.html %how not to design an mta - partitioning for security
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
705 http://fanf.livejournal.com/61132.html %how not to design an mta - local delivery
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
706 http://fanf.livejournal.com/64941.html %how not to design an mta - spool file format
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
707 http://fanf.livejournal.com/65203.html %how not to design an mta - spool file logistics
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
708 http://fanf.livejournal.com/65911.html %how not to design an mta - more about log-structured MTA queues
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
709 http://fanf.livejournal.com/67297.html %how not to design an mta - more log-structured MTA queues
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
710 http://fanf.livejournal.com/70432.html %how not to design an mta - address verification
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
711 http://fanf.livejournal.com/72258.html %how not to design an mta - content scanning
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
712
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
713
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
714
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
715
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
716
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
717
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
718
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
719
93
a6f8a93abd64 new chapter 4 (split ch5); added lots of annotations
meillo@marmaro.de
parents:
diff changeset
720
a6f8a93abd64 new chapter 4 (split ch5); added lots of annotations
meillo@marmaro.de
parents:
diff changeset
721
99
d24fdd3d5990 added lots of comments and annotations about what to do
meillo@marmaro.de
parents: 93
diff changeset
722
161
18b7b517e2dd wrote about discussion on architecture
meillo@marmaro.de
parents: 155
diff changeset
723 \section{Directions to go}
18b7b517e2dd wrote about discussion on architecture
meillo@marmaro.de
parents: 155
diff changeset
724
185
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
725 Now how could \masqmail\ be like in, say, five years?
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
726
161
18b7b517e2dd wrote about discussion on architecture
meillo@marmaro.de
parents: 155
diff changeset
727 This section discusses about what shapes \masqmail\ could have---which directions the development could go to.
18b7b517e2dd wrote about discussion on architecture
meillo@marmaro.de
parents: 155
diff changeset
728
93
a6f8a93abd64 new chapter 4 (split ch5); added lots of annotations
meillo@marmaro.de
parents:
diff changeset
729
185
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
730
146
2c4673d983c3 wrote about requirements (related to directions to go)
meillo@marmaro.de
parents: 142
diff changeset
731
185
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
732 1) fix the current version
146
2c4673d983c3 wrote about requirements (related to directions to go)
meillo@marmaro.de
parents: 142
diff changeset
733
163
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
734
185
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
735 2) create a new one
163
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
736 But how is the effort of this complete rewrite compared to what is gained afterwards?
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
737 << would one create it at all? >>
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
738
185
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
739
1611abd5443b restructuring and new content (a large commit)
meillo@marmaro.de
parents: 182
diff changeset
740 pro---contra
163
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
741
146
2c4673d983c3 wrote about requirements (related to directions to go)
meillo@marmaro.de
parents: 142
diff changeset
742
2c4673d983c3 wrote about requirements (related to directions to go)
meillo@marmaro.de
parents: 142
diff changeset
743
93
a6f8a93abd64 new chapter 4 (split ch5); added lots of annotations
meillo@marmaro.de
parents:
diff changeset
744
146
2c4673d983c3 wrote about requirements (related to directions to go)
meillo@marmaro.de
parents: 142
diff changeset
745 << short term goals --- long term goals >>
2c4673d983c3 wrote about requirements (related to directions to go)
meillo@marmaro.de
parents: 142
diff changeset
746
163
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
747 do it like sendmail: first do the most needed stuff on the old design to make it still usable. Then design a new version from scratch, for the future.
5681a18270b5 new content about architecture; some restructuring
meillo@marmaro.de
parents: 161
diff changeset
748
140
002fd18820cc small changes
meillo@marmaro.de
parents: 137
diff changeset
749 << which parts to take out and do within the thesis >>
93
a6f8a93abd64 new chapter 4 (split ch5); added lots of annotations
meillo@marmaro.de
parents:
diff changeset
750
167
74151e26ba6a this is the correct message for the last commit
meillo@marmaro.de
parents: 166
diff changeset
751