docs/diploma

annotate thesis/tex/4-MasqmailsFuture.tex @ 162:df6bfc48859b

I read, the correct US-american date is: Month dd, yyyy. So I removed the ^th
author meillo@marmaro.de
date Thu, 18 Dec 2008 11:32:31 +0100
parents 0b17f6e5edae
children 5681a18270b5
rev   line source
meillo@109 1 \chapter{\masqmail's present and future}
meillo@93 2
meillo@137 3 \section{Existing code base}
meillo@142 4 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.
meillo@142 5
meillo@93 6
meillo@137 7 \subsubsection*{Features}
meillo@93 8
meillo@142 9 \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.
meillo@93 10
meillo@142 11 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}.
meillo@137 12 %todo: what about SSL/TLS encryption?
meillo@93 13
meillo@142 14 \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.
meillo@142 15
meillo@137 16 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.
meillo@109 17 %masqmail: mailq, mailrm, runq, rmail, smtpd/in.smtpd
meillo@109 18 %sendmail: hoststat, mailq, newaliases, purgestat, smtpd
meillo@109 19
meillo@137 20 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.
meillo@109 21
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meillo@137 23
meillo@137 24 \subsubsection*{The code}
meillo@137 25
meillo@137 26 \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.
meillo@137 27
meillo@137 28 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.
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meillo@109 31 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.
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meillo@137 34 \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 a FIXME(holperig) code base.
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meillo@146 41 \section{Requirements}
meillo@146 42
meillo@146 43 Following is a list of current and future requirements to make \masqmail\ ready for the future.
meillo@146 44
meillo@146 45
meillo@146 46 \subsubsection*{Large message handling}
meillo@155 47 Trends in the market for electronic communication go towards consolidated communication, hence email will be used more to transfer voice and video messages. This leads to larger messages. The store-and-forward transport of email is not good suited for large data. Thus new protocols, like \NAME{QMTP} (described in section %\ref{FIXME}
meillo@155 48 ), may become popular.
meillo@146 49
meillo@146 50
meillo@146 51 \subsubsection*{Ressource friendly software}
meillo@149 52 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.
meillo@146 53
meillo@146 54
meillo@146 55 \subsubsection*{New mail transfer protocols}
meillo@149 56 Large messages demand more efficient transport through the net. As well is a final solution needed to defeat the spam problem. New mail transport protocols may be the only good solutions for both problems. They also can improve reliability, authentication, and verification issues. \masqmail\ should be able to support new protocols as they appear and are used.
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meillo@146 58
meillo@149 59 \subsubsection*{Spam handling}
meillo@149 60 Spam is a major threat. According to the \NAME{SWOT} analysis, the goal is to reduce it to a bearable level. 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.
meillo@146 61
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meillo@161 63 \subsubsection*{Security}
meillo@161 64 \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.
meillo@161 65
meillo@161 66
meillo@146 67 \subsubsection*{Easy configuration}
meillo@149 68 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.
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meillo@161 75 \section{Discussion on architecture}
meillo@146 76
meillo@161 77 A program's architecture is maybe the most influencing design decision, and has the greatest impact on the program's future capabilities. %fixme: search quote ... check if good
meillo@132 78
meillo@161 79 \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.
meillo@161 80
meillo@161 81 Figure \ref{fig:masqmail-arch} is an attempt to depict \masqmail's internal structure.
meillo@161 82
meillo@161 83 \begin{figure}
meillo@161 84 \begin{center}
meillo@161 85 \input{input/masqmail-arch.tex}
meillo@161 86 \end{center}
meillo@161 87 \caption{Internal architecture of \masqmail}
meillo@161 88 \label{fig:masqmail-arch}
meillo@161 89 \end{figure}
meillo@161 90
meillo@161 91 \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.
meillo@161 92
meillo@161 93 Every one of the popular \MTA{}s is more modular, or became more modular, than \masqmail. The logical step is to rewrite \masqmail\ using a modern, modular architecture to get a modern \MTA\ satisfying nowadays needs. But how is the effort of this complete rewrite compared to what is gained afterwards?
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meillo@161 98 A secure architecture is of need.
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meillo@161 106 (ssl)
meillo@161 107 -> msg-in (local or remote protocol handlers)
meillo@161 108 -> spam-filter (and more)
meillo@161 109 -> queue
meillo@161 110 -> msg-out (local-delivery by MDA, or remote-protocol-handlers)
meillo@161 111 (ssl)
meillo@161 112
meillo@161 113 A design from scratch?
meillo@161 114
meillo@161 115 << what would be needed (effort) >>
meillo@161 116
meillo@161 117 << would one create it at all? >>
meillo@161 118
meillo@161 119 << should it be done? >>
meillo@161 120
meillo@161 121
meillo@161 122 http://fanf.livejournal.com/50917.html %how not to design an mta - the sendmail command
meillo@161 123 http://fanf.livejournal.com/51349.html %how not to design an mta - partitioning for security
meillo@161 124 http://fanf.livejournal.com/61132.html %how not to design an mta - local delivery
meillo@161 125 http://fanf.livejournal.com/64941.html %how not to design an mta - spool file format
meillo@161 126 http://fanf.livejournal.com/65203.html %how not to design an mta - spool file logistics
meillo@161 127 http://fanf.livejournal.com/65911.html %how not to design an mta - more about log-structured MTA queues
meillo@161 128 http://fanf.livejournal.com/67297.html %how not to design an mta - more log-structured MTA queues
meillo@161 129 http://fanf.livejournal.com/70432.html %how not to design an mta - address verification
meillo@161 130 http://fanf.livejournal.com/72258.html %how not to design an mta - content scanning
meillo@161 131
meillo@161 132
meillo@161 133 \subsubsection*{local mail delivery}
meillo@161 134 But for example delivery of mail to local users is \emph{not} what \mta{}s should care about, although most \MTA\ are able to deliver mail, and many do. (\name{mail delivery agents}, like \name{procmail} and \name{maildrop}, are the right programs for this job.)
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meillo@149 140 \subsection{Access and Auth}
meillo@149 141
meillo@149 142 easiest: restricting by static IP addresses (Access control via hosts.allow/hosts.deny)
meillo@149 143 if dynamic remote hosts need access: some auth is needed
meillo@149 144 - SASL
meillo@149 145 - POP/IMAP: pop-before-smtp, DRAC, WHOSON
meillo@149 146 - TLS (certificates)
meillo@149 147
meillo@149 148 ``None of these add-ons is an ideal solution. They require additional code compiled into your existing daemons that may then require special write accesss to system files. They also require additional work for busy system administrators. If you cannot use any of the nonauthenticating alternatives mentioned earlier, or your business requirements demand that all of thyour users' mail pass through your system no matter where they are on the Internet, SASL is probably the solution that offers the most reliable and scalable method to authenticate users.'' (Dent: Postfix, page 44, ch04)
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meillo@149 152 postfix: after-queue-content-filter (smtp communication)
meillo@149 153 exim: content-scan-feature
meillo@149 154 sendmail: milter (tcp or unix sockets)
meillo@149 155
meillo@149 156 checks while smtp dialog (pre-queue): in MTA implemented (need to be fast)
meillo@149 157 checks when mail is accepted and queued: external (amavis, spamassassin)
meillo@149 158
meillo@149 159 anti-virus: clamav
meillo@149 160
meillo@149 161 AMaViS (amavisd-new): email filter framework to integrate spam and virus scanner
meillo@149 162 internet -->25 MTA -->10024 amavis -->10025 MTA --> reciptient
meillo@149 163 | |
meillo@149 164 +----------------------------+
meillo@149 165 mail scanner:
meillo@149 166 incoming queue --> mail scanner --> outgoing queue
meillo@149 167
meillo@149 168 mimedefang: uses milter interface with sendmail
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meillo@149 176 \subsection{spam and malicious content}
meillo@149 177
meillo@149 178 The same for malicious content (\name{malware}) like viruses, worms, trojan horses. They are related to spam, but affect the \MTA less, as they are in the mail body.
meillo@149 179
meillo@149 180 message body <-> envelope, header
meillo@149 181
meillo@149 182 where to filter what
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meillo@161 190 \section{Directions to go}
meillo@161 191
meillo@161 192 This section discusses about what shapes \masqmail\ could have---which directions the development could go to.
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meillo@146 198 \subsubsection*{\masqmail\ in five years}
meillo@146 199
meillo@146 200 Now how could \masqmail\ be like in, say, five years?
meillo@146 201
meillo@146 202 << plans to get masqmail more popular again (if that is the goal) >>
meillo@146 203
meillo@146 204 << More users >>
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meillo@93 209 \section{Work to do}
meillo@93 210
meillo@146 211 << short term goals --- long term goals >>
meillo@146 212
meillo@140 213 << which parts to take out and do within the thesis >>
meillo@93 214