Mercurial > docs > diploma

annotate thesis/tex/3-MailTransferAgents.tex @ 409:ca763bd8c809 default tip

Find changesets by keywords (author, files, the commit message), revision number or hash, or revset expression.
Added tag final version which I handed in for changeset ee7211546c02
author meillo@marmaro.de
date Wed, 11 Feb 2009 08:55:32 +0100
parents b357dfc509b5
children
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
rev   line source
89
3b5ba7331eb5 complete restructuring of whole document
meillo@marmaro.de
parents:
diff changeset
1 \chapter{Mail transfer agents}
254
db81f3cc6675 added thoughs about further dev ways
meillo@marmaro.de
parents: 248
diff changeset
2 \label{chap:mail-transfer-agents}
89
3b5ba7331eb5 complete restructuring of whole document
meillo@marmaro.de
parents:
diff changeset
3
377
90d5f98e3968 proof read ch03
meillo@marmaro.de
parents: 374
diff changeset
4 After having analyzed the market for email and having identified upcoming trends, in the last chapter; this chapter takes a look at \MTA{}s---the intelligent nodes and thus the most important parts of the email infrastructure. The \MTA{}s will be grouped by similarities first. Then the four most popular Free Software \MTA{}s will be presented to the reader in a short overview and with the most important facts. The end of this chapter is a short comparison of these programs.
89
3b5ba7331eb5 complete restructuring of whole document
meillo@marmaro.de
parents:
diff changeset
5
117
098bd0876934 worked on ch03 (MTAs)
meillo@marmaro.de
parents: 116
diff changeset
6
89
3b5ba7331eb5 complete restructuring of whole document
meillo@marmaro.de
parents:
diff changeset
7
3b5ba7331eb5 complete restructuring of whole document
meillo@marmaro.de
parents:
diff changeset
8
120
3b5e6ffd7b27 typographic cleanups
meillo@marmaro.de
parents: 119
diff changeset
9 \section{Types of MTAs}
391
16d8eacf60e1 created index (it is not finished)
meillo@marmaro.de
parents: 378
diff changeset
10
377
90d5f98e3968 proof read ch03
meillo@marmaro.de
parents: 374
diff changeset
11 ``Mail transfer agent'' is a term that covers a variety of programs. One thing is common to them: They transfer email from a sender to one or many recipients.
391
16d8eacf60e1 created index (it is not finished)
meillo@marmaro.de
parents: 378
diff changeset
12 \index{mta!definition}
89
3b5ba7331eb5 complete restructuring of whole document
meillo@marmaro.de
parents:
diff changeset
13
373
d51894e48762 started indexing; mta -> MTA (many small changes)
meillo@marmaro.de
parents: 364
diff changeset
14 This is how \person{Bryan Costales} defines an \MTA:
377
90d5f98e3968 proof read ch03
meillo@marmaro.de
parents: 374
diff changeset
15
117
098bd0876934 worked on ch03 (MTAs)
meillo@marmaro.de
parents: 116
diff changeset
16 \begin{quote}
217
d645ac015c3b a lot of rework
meillo@marmaro.de
parents: 211
diff changeset
17 A mail transfer agent (\MTA) is a highly specialized program that delivers mail and transports it between machines, like the post office.
218
711f0d3f5dfd minor change for block quotes
meillo@marmaro.de
parents: 217
diff changeset
18 \hfill\cite{costales97}
117
098bd0876934 worked on ch03 (MTAs)
meillo@marmaro.de
parents: 116
diff changeset
19 \end{quote}
377
90d5f98e3968 proof read ch03
meillo@marmaro.de
parents: 374
diff changeset
20
217
d645ac015c3b a lot of rework
meillo@marmaro.de
parents: 211
diff changeset
21 \name{The Free Dictionary} is a bit more concrete on the term:
377
90d5f98e3968 proof read ch03
meillo@marmaro.de
parents: 374
diff changeset
22
117
098bd0876934 worked on ch03 (MTAs)
meillo@marmaro.de
parents: 116
diff changeset
23 \begin{quote}
217
d645ac015c3b a lot of rework
meillo@marmaro.de
parents: 211
diff changeset
24 Message Transfer Agent - (\MTA, Mail Transfer Agent): Any program responsible for delivering e-mail messages. Upon receiving a message from a Mail User Agent or another \MTA, [...] it [...] delivers it to any local addressees and/or forwards it to other remote \MTA{}s (routing) for delivery to remote recipients.
218
711f0d3f5dfd minor change for block quotes
meillo@marmaro.de
parents: 217
diff changeset
25 \hfill\citeweb{website:thefreedictionary}
117
098bd0876934 worked on ch03 (MTAs)
meillo@marmaro.de
parents: 116
diff changeset
26 \end{quote}
89
3b5ba7331eb5 complete restructuring of whole document
meillo@marmaro.de
parents:
diff changeset
27
259
5db159540ba8 moved some text
meillo@marmaro.de
parents: 254
diff changeset
28 \person{Dent} and \person{Hafiz} agree \cite[page 19]{dent04} \cite[pages 3-5]{hafiz05}.
5db159540ba8 moved some text
meillo@marmaro.de
parents: 254
diff changeset
29
377
90d5f98e3968 proof read ch03
meillo@marmaro.de
parents: 374
diff changeset
30 Common to all \MTA{}s is the transport of mail; this is the actual job. Besides this similarity, \MTA{}s can be very different. Some of them have \NAME{POP3} and/or \NAME{IMAP} servers included. Some can fetch mails through these protocols. Others have all features one can think of. And maybe there are some that do nothing else but transporting email.
391
16d8eacf60e1 created index (it is not finished)
meillo@marmaro.de
parents: 378
diff changeset
31 \index{pop3}
16d8eacf60e1 created index (it is not finished)
meillo@marmaro.de
parents: 378
diff changeset
32 \index{imap}
117
098bd0876934 worked on ch03 (MTAs)
meillo@marmaro.de
parents: 116
diff changeset
33
373
d51894e48762 started indexing; mta -> MTA (many small changes)
meillo@marmaro.de
parents: 364
diff changeset
34 Following is a classification of \MTA{}s into groups of similar programs, regarding what is viewable from the outside.
117
098bd0876934 worked on ch03 (MTAs)
meillo@marmaro.de
parents: 116
diff changeset
35
098bd0876934 worked on ch03 (MTAs)
meillo@marmaro.de
parents: 116
diff changeset
36
120
3b5e6ffd7b27 typographic cleanups
meillo@marmaro.de
parents: 119
diff changeset
37 \subsubsection*{Relay-only MTAs}
89
3b5ba7331eb5 complete restructuring of whole document
meillo@marmaro.de
parents:
diff changeset
38 \label{subsec:relay-only}
377
90d5f98e3968 proof read ch03
meillo@marmaro.de
parents: 374
diff changeset
39
90d5f98e3968 proof read ch03
meillo@marmaro.de
parents: 374
diff changeset
40 Also called \name{forwarders}. This is the most simple kind of an \MTA. It transfers mail only to defined \name{smart hosts}\footnote{\name{smart host}s are mail servers that receive email and route it to the actual destination.}. Relay-only \MTA{}s do not receive mail from outside the system and they do not deliver locally. All they do is transfer mail to a specified smart host for further relay.
391
16d8eacf60e1 created index (it is not finished)
meillo@marmaro.de
parents: 378
diff changeset
41 \index{relay-only mta}
16d8eacf60e1 created index (it is not finished)
meillo@marmaro.de
parents: 378
diff changeset
42 \index{smart host}
89
3b5ba7331eb5 complete restructuring of whole document
meillo@marmaro.de
parents:
diff changeset
43
3b5ba7331eb5 complete restructuring of whole document
meillo@marmaro.de
parents:
diff changeset
44 Most \MTA{}s can be configured to act as such a \name{forwarder}. But this is usually an additional functionality.
3b5ba7331eb5 complete restructuring of whole document
meillo@marmaro.de
parents:
diff changeset
45
377
90d5f98e3968 proof read ch03
meillo@marmaro.de
parents: 374
diff changeset
46 One uses this kind of \MTA\ to give a system the possibility to send mail without the need to do a lot of configuration. In a local network, usually the clients are set up with relay-only \MTA{}s, while there is one mail server that acts as a smart host. The ``dumb'' clients send mail to this mail server which does all further work.
89
3b5ba7331eb5 complete restructuring of whole document
meillo@marmaro.de
parents:
diff changeset
47
377
90d5f98e3968 proof read ch03
meillo@marmaro.de
parents: 374
diff changeset
48 Example programs in that group are: \name{nullmailer}, \name{ssmtp}, and \name{esmtp}.
89
3b5ba7331eb5 complete restructuring of whole document
meillo@marmaro.de
parents:
diff changeset
49
3b5ba7331eb5 complete restructuring of whole document
meillo@marmaro.de
parents:
diff changeset
50
117
098bd0876934 worked on ch03 (MTAs)
meillo@marmaro.de
parents: 116
diff changeset
51 \subsubsection*{Groupware}
391
16d8eacf60e1 created index (it is not finished)
meillo@marmaro.de
parents: 378
diff changeset
52 \index{groupware}
16d8eacf60e1 created index (it is not finished)
meillo@marmaro.de
parents: 378
diff changeset
53
377
90d5f98e3968 proof read ch03
meillo@marmaro.de
parents: 374
diff changeset
54 Normally the term ``groupware'' does not mean one single program, but a suite of programs. They build a framework which is then populated with various modules that provide the actual functionality. Modules for mail transfer, file storage, calendars, resource management, Instant Messaging, and more, are commonly available.
89
3b5ba7331eb5 complete restructuring of whole document
meillo@marmaro.de
parents:
diff changeset
55
392
b4611d4e1484 applied comments by henry atting
meillo@marmaro.de
parents: 391
diff changeset
56 These program suites are used if the main work to do is providing integrated communication facilities and team working support for a group of people. Mail transfer is only one part of the problem to solve. The most common scenario are companies. They use \name{groupware} to provide adequate services for their teams to work efficiently. But one may use \name{groupware} on the home server for the family members, too.
89
3b5ba7331eb5 complete restructuring of whole document
meillo@marmaro.de
parents:
diff changeset
57
377
90d5f98e3968 proof read ch03
meillo@marmaro.de
parents: 374
diff changeset
58 Examples for groupware are: \name{Lotus Notes}, \name{Microsoft Exchange}, and \name{OpenGroupware.org}.
89
3b5ba7331eb5 complete restructuring of whole document
meillo@marmaro.de
parents:
diff changeset
59
3b5ba7331eb5 complete restructuring of whole document
meillo@marmaro.de
parents:
diff changeset
60
120
3b5e6ffd7b27 typographic cleanups
meillo@marmaro.de
parents: 119
diff changeset
61 \subsubsection*{``Real'' MTAs}
402
e57129f57faa finished the indexing in a huge last effort
meillo@marmaro.de
parents: 400
diff changeset
62 \index{mta!real ones}
391
16d8eacf60e1 created index (it is not finished)
meillo@marmaro.de
parents: 378
diff changeset
63
373
d51894e48762 started indexing; mta -> MTA (many small changes)
meillo@marmaro.de
parents: 364
diff changeset
64 There is a third type of \MTA{}s in between the minimalistic \name{relay-only} \MTA{}s and the feature loaded \name{groupware}. Those programs may be named ``real \MTA{}s'', or ``proper \MTA{}s'', though there is no common name. They are what is meant with the term ``mail transfer agent''---programs that transfer mail between hosts.
89
3b5ba7331eb5 complete restructuring of whole document
meillo@marmaro.de
parents:
diff changeset
65
377
90d5f98e3968 proof read ch03
meillo@marmaro.de
parents: 374
diff changeset
66 Common to them is their focus on the email transfer, while they are able to act as smart hosts. Their variety ranges from ones mostly restricted to mail transfer (e.g.\ \qmail) to others having interfaces for adding further mail processing modules (e.g.\ \postfix). This group covers everything in between the other two groups.
89
3b5ba7331eb5 complete restructuring of whole document
meillo@marmaro.de
parents:
diff changeset
67
377
90d5f98e3968 proof read ch03
meillo@marmaro.de
parents: 374
diff changeset
68 \name{Real} \MTA{}s include \sendmail, \exim, \qmail, and \postfix.
402
e57129f57faa finished the indexing in a huge last effort
meillo@marmaro.de
parents: 400
diff changeset
69 \index{sendmail}
e57129f57faa finished the indexing in a huge last effort
meillo@marmaro.de
parents: 400
diff changeset
70 \index{postfix}
e57129f57faa finished the indexing in a huge last effort
meillo@marmaro.de
parents: 400
diff changeset
71 \index{qmail}
e57129f57faa finished the indexing in a huge last effort
meillo@marmaro.de
parents: 400
diff changeset
72 \index{exim}
89
3b5ba7331eb5 complete restructuring of whole document
meillo@marmaro.de
parents:
diff changeset
73
3b5ba7331eb5 complete restructuring of whole document
meillo@marmaro.de
parents:
diff changeset
74
117
098bd0876934 worked on ch03 (MTAs)
meillo@marmaro.de
parents: 116
diff changeset
75 \subsubsection*{Other segmenting}
391
16d8eacf60e1 created index (it is not finished)
meillo@marmaro.de
parents: 378
diff changeset
76
377
90d5f98e3968 proof read ch03
meillo@marmaro.de
parents: 374
diff changeset
77 \MTA{}s can also be split in other ways.
308
273f2d174315 small rework
meillo@marmaro.de
parents: 287
diff changeset
78
396
8ef85e22ff7d again lots of fixes and removed fixmes
meillo@marmaro.de
parents: 394
diff changeset
79 Due to \sendmail's significance in the early times of email, compatibility interfaces to \sendmail\ are important for Unix \MTA{}s. The reason is that many mail applications simply assume the \sendmail\ \MTA\ to be installed on the system. Being not \name{sendmail-compatible} may not matter for some fields of action, but makes the program ineligible for serving as a general purpose \MTA\ on Unix systems. Hence being sendmail-compatible is a major property of an \MTA. \MTA{}s without \name{sendmail-compatible} interfaces, or at least compatibility add-ons, will not be covered here. One example for such a program is \name{Apache James}.
391
16d8eacf60e1 created index (it is not finished)
meillo@marmaro.de
parents: 378
diff changeset
80 \index{sendmail!compatibility}
402
e57129f57faa finished the indexing in a huge last effort
meillo@marmaro.de
parents: 400
diff changeset
81 \index{Unix}
89
3b5ba7331eb5 complete restructuring of whole document
meillo@marmaro.de
parents:
diff changeset
82
377
90d5f98e3968 proof read ch03
meillo@marmaro.de
parents: 374
diff changeset
83 Another separation can be done between Free Software \MTA{}s and proprietary ones. Many of the \MTA{}s for Unix systems are Free Software. Only these are regarded throughout this thesis, because comparing Free Software with proprietary or commercial software is not what typical users of programs like \masqmail\ do. Comparison with non-free programs may be a point for large Free Software projects that try to step into the business world. Small projects, mostly used by individuals at home, need to be compared against other projects of similar shape. The document is seen from \masqmail's point of view---an \MTA\ for Unix systems on home servers and workstations---so non-free software is out of the way.
402
e57129f57faa finished the indexing in a huge last effort
meillo@marmaro.de
parents: 400
diff changeset
84 \index{Free Software}
e57129f57faa finished the indexing in a huge last effort
meillo@marmaro.de
parents: 400
diff changeset
85 \index{Free Software projects}
89
3b5ba7331eb5 complete restructuring of whole document
meillo@marmaro.de
parents:
diff changeset
86
3b5ba7331eb5 complete restructuring of whole document
meillo@marmaro.de
parents:
diff changeset
87
3b5ba7331eb5 complete restructuring of whole document
meillo@marmaro.de
parents:
diff changeset
88
3b5ba7331eb5 complete restructuring of whole document
meillo@marmaro.de
parents:
diff changeset
89
265
6ed93483bba9 added section about masqmails position
meillo@marmaro.de
parents: 259
diff changeset
90
6ed93483bba9 added section about masqmails position
meillo@marmaro.de
parents: 259
diff changeset
91
6ed93483bba9 added section about masqmails position
meillo@marmaro.de
parents: 259
diff changeset
92 \subsubsection*{\masqmail's position}
402
e57129f57faa finished the indexing in a huge last effort
meillo@marmaro.de
parents: 400
diff changeset
93 \index{masqmail!position}
265
6ed93483bba9 added section about masqmails position
meillo@marmaro.de
parents: 259
diff changeset
94
377
90d5f98e3968 proof read ch03
meillo@marmaro.de
parents: 374
diff changeset
95 Now, where does \masqmail\ fit in? It is not groupware nor a simple forwarder, thus it belongs to the ``real \MTA{}s''. Additionally, it is Free Software and is sendmail-compatible to a large degree. This makes it similar to \sendmail, \exim, \qmail, and \postfix. \masqmail\ is intended to be a replacement for those \MTA{}s.
265
6ed93483bba9 added section about masqmails position
meillo@marmaro.de
parents: 259
diff changeset
96
378
c9a6cbce35fd inserted non-break spaces where appropriate
meillo@marmaro.de
parents: 377
diff changeset
97 But: It was not designed to be used as a general replacement for them. (See: section~\ref{sec:masqmail-target-field}) In fact, \masqmail\ is only a replacement \emph{in some situations}. This primary excludes working in an untrusted environment.
265
6ed93483bba9 added section about masqmails position
meillo@marmaro.de
parents: 259
diff changeset
98
6ed93483bba9 added section about masqmails position
meillo@marmaro.de
parents: 259
diff changeset
99
6ed93483bba9 added section about masqmails position
meillo@marmaro.de
parents: 259
diff changeset
100
6ed93483bba9 added section about masqmails position
meillo@marmaro.de
parents: 259
diff changeset
101
6ed93483bba9 added section about masqmails position
meillo@marmaro.de
parents: 259
diff changeset
102
6ed93483bba9 added section about masqmails position
meillo@marmaro.de
parents: 259
diff changeset
103
6ed93483bba9 added section about masqmails position
meillo@marmaro.de
parents: 259
diff changeset
104
6ed93483bba9 added section about masqmails position
meillo@marmaro.de
parents: 259
diff changeset
105
6ed93483bba9 added section about masqmails position
meillo@marmaro.de
parents: 259
diff changeset
106
6ed93483bba9 added section about masqmails position
meillo@marmaro.de
parents: 259
diff changeset
107
120
3b5e6ffd7b27 typographic cleanups
meillo@marmaro.de
parents: 119
diff changeset
108 \section{Popular MTAs}
117
098bd0876934 worked on ch03 (MTAs)
meillo@marmaro.de
parents: 116
diff changeset
109
393
6494832a798c fixed all half-spaces after RF, RG, TODO
meillo@marmaro.de
parents: 392
diff changeset
110 This section introduces a selection of popular \MTA{}s; they are the most likely substitutes for \masqmail. All are sendmail-compatible ``smart'' Free Software \MTA{}s that focus on mail transfer, as is \masqmail.
89
3b5ba7331eb5 complete restructuring of whole document
meillo@marmaro.de
parents:
diff changeset
111
377
90d5f98e3968 proof read ch03
meillo@marmaro.de
parents: 374
diff changeset
112 The programs chosen to be compared are: \sendmail, \exim, \qmail, and \postfix. They are the most important representatives of the regarded group.
402
e57129f57faa finished the indexing in a huge last effort
meillo@marmaro.de
parents: 400
diff changeset
113 \index{sendmail}
e57129f57faa finished the indexing in a huge last effort
meillo@marmaro.de
parents: 400
diff changeset
114 \index{postfix}
e57129f57faa finished the indexing in a huge last effort
meillo@marmaro.de
parents: 400
diff changeset
115 \index{qmail}
e57129f57faa finished the indexing in a huge last effort
meillo@marmaro.de
parents: 400
diff changeset
116 \index{exim}
130
6ce355da579f market share stuff and more
meillo@marmaro.de
parents: 128
diff changeset
117
145
93a47593a493 changed order of mta stats cols; added subsection headings
meillo@marmaro.de
parents: 143
diff changeset
118
93a47593a493 changed order of mta stats cols; added subsection headings
meillo@marmaro.de
parents: 143
diff changeset
119 \subsection{Market share analysis}
323
82496704f747 added labels
meillo@marmaro.de
parents: 321
diff changeset
120 \label{sec:market-share}
402
e57129f57faa finished the indexing in a huge last effort
meillo@marmaro.de
parents: 400
diff changeset
121 \index{mta!market share}
145
93a47593a493 changed order of mta stats cols; added subsection headings
meillo@marmaro.de
parents: 143
diff changeset
122
377
90d5f98e3968 proof read ch03
meillo@marmaro.de
parents: 374
diff changeset
123 \MTA\ statistics are rare, differ, and good data is hard to collect. These points are bad if good statistics are wanted. Thus it is obvious there are only few available.
217
d645ac015c3b a lot of rework
meillo@marmaro.de
parents: 211
diff changeset
124
378
c9a6cbce35fd inserted non-break spaces where appropriate
meillo@marmaro.de
parents: 377
diff changeset
125 Table~\ref{tab:mta-market-share} shows the most used \MTA{}s determined by three different statistics. The first was done by \person{Daniel~J.\ Bernstein} (the author of \qmail) in 2001 \cite{bernstein01}. The second is by \person{Simpson} and \person{Bekman} in 2007 and was published on \name{O'ReillyNet} \cite{simpson07}. And the third is from \name{MailRadar.com} with unknown date\footnote{The footer of the website shows ``Copyright 2007'' but more likely does this refer to the whole website.} \citeweb{mailradar:mta-stats}.
89
3b5ba7331eb5 complete restructuring of whole document
meillo@marmaro.de
parents:
diff changeset
126
130
6ce355da579f market share stuff and more
meillo@marmaro.de
parents: 128
diff changeset
127 \begin{table}
6ce355da579f market share stuff and more
meillo@marmaro.de
parents: 128
diff changeset
128 \begin{center}
271
c80b6b6fb798 moved tables from input to tbl
meillo@marmaro.de
parents: 265
diff changeset
129 \input{tbl/mta-market-share.tbl}
130
6ce355da579f market share stuff and more
meillo@marmaro.de
parents: 128
diff changeset
130 \end{center}
6ce355da579f market share stuff and more
meillo@marmaro.de
parents: 128
diff changeset
131 \caption{Market share of \MTA{}s}
6ce355da579f market share stuff and more
meillo@marmaro.de
parents: 128
diff changeset
132 \label{tab:mta-market-share}
6ce355da579f market share stuff and more
meillo@marmaro.de
parents: 128
diff changeset
133 \end{table}
117
098bd0876934 worked on ch03 (MTAs)
meillo@marmaro.de
parents: 116
diff changeset
134
373
d51894e48762 started indexing; mta -> MTA (many small changes)
meillo@marmaro.de
parents: 364
diff changeset
135 All surveys show high market shares for the four \MTA{}s: \sendmail, \exim, \qmail, and \postfix. Only the \name{Microsoft} mail server software and \name{IMail} have comparable large shares. Other Free Software \MTA{}s (\name{smail}, \name{zmailer}, \NAME{MMDF}, \name{courier-mta}) are less important and seldom used.
402
e57129f57faa finished the indexing in a huge last effort
meillo@marmaro.de
parents: 400
diff changeset
136 \index{mmdf}
e57129f57faa finished the indexing in a huge last effort
meillo@marmaro.de
parents: 400
diff changeset
137 \index{smail}
e57129f57faa finished the indexing in a huge last effort
meillo@marmaro.de
parents: 400
diff changeset
138 \index{zmailer}
e57129f57faa finished the indexing in a huge last effort
meillo@marmaro.de
parents: 400
diff changeset
139 \index{courier-mta}
145
93a47593a493 changed order of mta stats cols; added subsection headings
meillo@marmaro.de
parents: 143
diff changeset
140
377
90d5f98e3968 proof read ch03
meillo@marmaro.de
parents: 374
diff changeset
141 The three surveys base on different data. \person{Bernstein} took 1\,000\,000 randomly chosen \NAME{IP} addresses, containing 39\,206 valid hosts; 958 of them accepted \NAME{SMTP} connections. The \name{O'ReillyNet} survey used only domains owned by companies; in total 400\,000 hosts. \name{MailRadar} scanned 2\,818\,895 servers, leading to 59\,209 accepted connections.
145
93a47593a493 changed order of mta stats cols; added subsection headings
meillo@marmaro.de
parents: 143
diff changeset
142
377
90d5f98e3968 proof read ch03
meillo@marmaro.de
parents: 374
diff changeset
143 All surveys show \sendmail\ to be the most popular \MTA. \postfix, \qmail, and \exim\ are among the top six in each. \exim\ has slightly smaller shares than the other two. The four programs together share more than half of the market according to \person{Bernstein} and the \name{MailRadar} statistics. \name{O'ReillyNet} has their share to be somewhere between a third and the half. This uncertainty comes from the large amount of unidentifiable \MTA{}s.
402
e57129f57faa finished the indexing in a huge last effort
meillo@marmaro.de
parents: 400
diff changeset
144 \index{sendmail}
e57129f57faa finished the indexing in a huge last effort
meillo@marmaro.de
parents: 400
diff changeset
145 \index{postfix}
e57129f57faa finished the indexing in a huge last effort
meillo@marmaro.de
parents: 400
diff changeset
146 \index{qmail}
e57129f57faa finished the indexing in a huge last effort
meillo@marmaro.de
parents: 400
diff changeset
147 \index{exim}
143
70201774b457 work on market share analysis
meillo@marmaro.de
parents: 140
diff changeset
148
377
90d5f98e3968 proof read ch03
meillo@marmaro.de
parents: 374
diff changeset
149 The 22 percent of \name{mail security layers} in the \name{O'ReillyNet} survey is remarkable. Mail security layers are software guards between the network and the \MTA\ that filter unwanted mail before it reaches the \MTA. This increases security by filtering malicious content and by blocking attacks against the \MTA. The large share here may be a result of only regarding business mail servers. The problem concerning the survey is the disguise of the \MTA{}s that run behind the security layer. It seems wrong to assume equal shares for the \MTA{}s behind the guards as for the unguarded \MTA{}s, because mail security layers will be more often used to guard weak \MTA{}s, as strong ones do not need them so much. This needs to be kept in mind when looking at the \name{O'ReillyNet} survey.
391
16d8eacf60e1 created index (it is not finished)
meillo@marmaro.de
parents: 378
diff changeset
150 \index{mail security layer}
143
70201774b457 work on market share analysis
meillo@marmaro.de
parents: 140
diff changeset
151
377
90d5f98e3968 proof read ch03
meillo@marmaro.de
parents: 374
diff changeset
152 The date of the \name{Mailradar} statistics is not known; a mail to \name{Mailradar} with a request for information has not been replied, unfortunately. However, it seems quite sure that the statistics were published after 2001, caused by the \sendmail\ and \postfix\ shares. But to decide whether before or after the one from \name{O'ReillyNet} would be just guessing. Possibly it receives constant input and thus displays a current state.
89
3b5ba7331eb5 complete restructuring of whole document
meillo@marmaro.de
parents:
diff changeset
153
130
6ce355da579f market share stuff and more
meillo@marmaro.de
parents: 128
diff changeset
154
145
93a47593a493 changed order of mta stats cols; added subsection headings
meillo@marmaro.de
parents: 143
diff changeset
155 \subsection{The four major Free Software MTAs}
402
e57129f57faa finished the indexing in a huge last effort
meillo@marmaro.de
parents: 400
diff changeset
156 \index{Free Software}
145
93a47593a493 changed order of mta stats cols; added subsection headings
meillo@marmaro.de
parents: 143
diff changeset
157
378
c9a6cbce35fd inserted non-break spaces where appropriate
meillo@marmaro.de
parents: 377
diff changeset
158 Now follows a small introduction to the four programs chosen for comparison. \masqmail\ is not presented here as it was already introduced in chapter~\ref{chap:introduction}. Longer introductions, including analysis and comparison, were written by \person{Jonathan de Boyne Pollard} \cite{jdebp}.
117
098bd0876934 worked on ch03 (MTAs)
meillo@marmaro.de
parents: 116
diff changeset
159
89
3b5ba7331eb5 complete restructuring of whole document
meillo@marmaro.de
parents:
diff changeset
160
117
098bd0876934 worked on ch03 (MTAs)
meillo@marmaro.de
parents: 116
diff changeset
161
120
3b5e6ffd7b27 typographic cleanups
meillo@marmaro.de
parents: 119
diff changeset
162 \subsubsection*{sendmail}
89
3b5ba7331eb5 complete restructuring of whole document
meillo@marmaro.de
parents:
diff changeset
163 \label{sec:sendmail}
391
16d8eacf60e1 created index (it is not finished)
meillo@marmaro.de
parents: 378
diff changeset
164 \index{sendmail}
89
3b5ba7331eb5 complete restructuring of whole document
meillo@marmaro.de
parents:
diff changeset
165
377
90d5f98e3968 proof read ch03
meillo@marmaro.de
parents: 374
diff changeset
166 \sendmail\ is the best known \MTA, since it was one of the first and surely the one that made \MTA{}s popular. It also was shipped as default \MTA{}s by many Unix system vendors \citeweb{wikipedia:sendmail}.
402
e57129f57faa finished the indexing in a huge last effort
meillo@marmaro.de
parents: 400
diff changeset
167 \index{Unix}
377
90d5f98e3968 proof read ch03
meillo@marmaro.de
parents: 374
diff changeset
168
90d5f98e3968 proof read ch03
meillo@marmaro.de
parents: 374
diff changeset
169 The program was written by \person{Eric Allman} as the successor of his program \name{delivermail}. \person{Allman} was not the only one who was working on the program. Other people developed own versions of it and a variety of flavors came up, especially in the late eighties when Allman was inactive \cite[page~5]{vixie01}.
402
e57129f57faa finished the indexing in a huge last effort
meillo@marmaro.de
parents: 400
diff changeset
170 \index{delivermail}
89
3b5ba7331eb5 complete restructuring of whole document
meillo@marmaro.de
parents:
diff changeset
171
377
90d5f98e3968 proof read ch03
meillo@marmaro.de
parents: 374
diff changeset
172 \sendmail\ is designed to transfer mails between different protocols and networks, this lead to a very flexible, though complex, configuration.
89
3b5ba7331eb5 complete restructuring of whole document
meillo@marmaro.de
parents:
diff changeset
173
377
90d5f98e3968 proof read ch03
meillo@marmaro.de
parents: 374
diff changeset
174 The program was first released with \NAME{BSD} 4.1c in 1983. The latest version is 8.14.3 from May 2008. The program is distributed under the \name{Sendmail License} as both, free and proprietary software.
391
16d8eacf60e1 created index (it is not finished)
meillo@marmaro.de
parents: 378
diff changeset
175 \index{bsd}
312
a62fe460b8de work in MTA comparison
meillo@marmaro.de
parents: 308
diff changeset
176
378
c9a6cbce35fd inserted non-break spaces where appropriate
meillo@marmaro.de
parents: 377
diff changeset
177 Further development will go into the project \name{MeTA1} which succeeds \sendmail. The former name of this new project was \name{sendmail~X}.
402
e57129f57faa finished the indexing in a huge last effort
meillo@marmaro.de
parents: 400
diff changeset
178 \index{sendmail!meta1}
e57129f57faa finished the indexing in a huge last effort
meillo@marmaro.de
parents: 400
diff changeset
179 \index{sendmail!sendmailx}
89
3b5ba7331eb5 complete restructuring of whole document
meillo@marmaro.de
parents:
diff changeset
180
377
90d5f98e3968 proof read ch03
meillo@marmaro.de
parents: 374
diff changeset
181 More information can be found on the \sendmail\ homepage \citeweb{sendmail:homepage} and in the, so called, \name{Bat Book} \cite{costales97}.
89
3b5ba7331eb5 complete restructuring of whole document
meillo@marmaro.de
parents:
diff changeset
182
3b5ba7331eb5 complete restructuring of whole document
meillo@marmaro.de
parents:
diff changeset
183
117
098bd0876934 worked on ch03 (MTAs)
meillo@marmaro.de
parents: 116
diff changeset
184
120
3b5e6ffd7b27 typographic cleanups
meillo@marmaro.de
parents: 119
diff changeset
185 \subsubsection*{exim}
117
098bd0876934 worked on ch03 (MTAs)
meillo@marmaro.de
parents: 116
diff changeset
186 \label{sec:exim}
391
16d8eacf60e1 created index (it is not finished)
meillo@marmaro.de
parents: 378
diff changeset
187 \index{exim}
117
098bd0876934 worked on ch03 (MTAs)
meillo@marmaro.de
parents: 116
diff changeset
188
377
90d5f98e3968 proof read ch03
meillo@marmaro.de
parents: 374
diff changeset
189 \exim\ was started in 1995 by \person{Philip Hazel} at the \name{University of Cambridge}. It is a fork of \name{smail-3}, and inherited the monolithic architecture which is similar to \sendmail's. But having no architecture-given separation of the individual components of the system did not hurt. Its security is quite good \cite{blanco05}.
402
e57129f57faa finished the indexing in a huge last effort
meillo@marmaro.de
parents: 400
diff changeset
190 \index{smail}
377
90d5f98e3968 proof read ch03
meillo@marmaro.de
parents: 374
diff changeset
191
392
b4611d4e1484 applied comments by henry atting
meillo@marmaro.de
parents: 391
diff changeset
192 \exim\ is highly configurable, especially in the field of mail policies. This makes it easy to specify how mail is routed through the system and who is allowed to send email to whom. Interfaces to integrate spam and malware checkers are provided by design, too.
117
098bd0876934 worked on ch03 (MTAs)
meillo@marmaro.de
parents: 116
diff changeset
193
391
16d8eacf60e1 created index (it is not finished)
meillo@marmaro.de
parents: 378
diff changeset
194 The program is Free Software, released under the \NAME{GPL}. The latest stable version is 4.69 from December 2007.
16d8eacf60e1 created index (it is not finished)
meillo@marmaro.de
parents: 378
diff changeset
195 \index{gpl}
117
098bd0876934 worked on ch03 (MTAs)
meillo@marmaro.de
parents: 116
diff changeset
196
217
d645ac015c3b a lot of rework
meillo@marmaro.de
parents: 211
diff changeset
197 One finds \exim\ on its homepage \citeweb{exim:homepage}. The standard literature is \person{Hazel}'s \exim\ book \cite{hazel01}.
117
098bd0876934 worked on ch03 (MTAs)
meillo@marmaro.de
parents: 116
diff changeset
198
098bd0876934 worked on ch03 (MTAs)
meillo@marmaro.de
parents: 116
diff changeset
199
098bd0876934 worked on ch03 (MTAs)
meillo@marmaro.de
parents: 116
diff changeset
200
120
3b5e6ffd7b27 typographic cleanups
meillo@marmaro.de
parents: 119
diff changeset
201 \subsubsection*{qmail}
89
3b5ba7331eb5 complete restructuring of whole document
meillo@marmaro.de
parents:
diff changeset
202 \label{sec:qmail}
391
16d8eacf60e1 created index (it is not finished)
meillo@marmaro.de
parents: 378
diff changeset
203 \index{qmail}
377
90d5f98e3968 proof read ch03
meillo@marmaro.de
parents: 374
diff changeset
204
90d5f98e3968 proof read ch03
meillo@marmaro.de
parents: 374
diff changeset
205 \qmail\ is seen by its community as ``a modern \SMTP\ server which makes sendmail obsolete'' \citeweb{qmail:homepage2}. It was written by \person{Daniel~J.\ Bernstein}, starting in 1995. His primary goal was to create a secure \MTA\ to replace the popular, but vulnerable, \sendmail. His own words are: ``This is why I started writing qmail: I was sick of the security holes in sendmail and other \MTA{}s.'' \citeweb{qmail:homepage1}.
402
e57129f57faa finished the indexing in a huge last effort
meillo@marmaro.de
parents: 400
diff changeset
206 \index{sendmail}
89
3b5ba7331eb5 complete restructuring of whole document
meillo@marmaro.de
parents:
diff changeset
207
392
b4611d4e1484 applied comments by henry atting
meillo@marmaro.de
parents: 391
diff changeset
208 \qmail\ first introduced many innovative concepts in \MTA\ design. The most obvious contrast to \sendmail\ and \exim\ is its modular design. But \qmail\ was not the first modular \MTA. \NAME{MMDF}, which predates even \sendmail, was modular, too. Regardless of \NAME{MMDF}'s modular architecture, \qmail\ is generally seen as the first security-aware \MTA\ \citeweb{wikipedia:qmail}.
402
e57129f57faa finished the indexing in a huge last effort
meillo@marmaro.de
parents: 400
diff changeset
209 \index{exim}
e57129f57faa finished the indexing in a huge last effort
meillo@marmaro.de
parents: 400
diff changeset
210 \index{mmdf}
223
f88853595b7a reworked section about qmail
meillo@marmaro.de
parents: 218
diff changeset
211
377
90d5f98e3968 proof read ch03
meillo@marmaro.de
parents: 374
diff changeset
212 The latest release of \qmail\ is version 1.03 from July 1998. Afterwards, in November 2007, \qmail's source was put into the \name{public domain}. This made it Free Software.
89
3b5ba7331eb5 complete restructuring of whole document
meillo@marmaro.de
parents:
diff changeset
213
377
90d5f98e3968 proof read ch03
meillo@marmaro.de
parents: 374
diff changeset
214 Because of \person{Bernstein}'s inactivity, though the requirements changed since 1998, ``[a] motley krewe of qmail contributors (see the \NAME{README}) has put together a netqmail-1.06 distribution of qmail. It is derived from Daniel Bernstein's qmail-1.03 plus bug fixes, a few feature enhancements, and some documentation.'' \citeweb{netqmail:homepage}.
402
e57129f57faa finished the indexing in a huge last effort
meillo@marmaro.de
parents: 400
diff changeset
215 \index{qmail!netqmail}
89
3b5ba7331eb5 complete restructuring of whole document
meillo@marmaro.de
parents:
diff changeset
216
248
724cc6057105 complete names are now in small caps
meillo@marmaro.de
parents: 225
diff changeset
217 \qmail's homepages are \citeweb{qmail:homepage1} and \citeweb{qmail:homepage2}. The best book about \qmail, from \person{Bernstein}'s view, is \person{Dave Sill}'s handbook \cite{sill02}. His free available guide ``Life with qmail'' is another valuable source \cite{lifewithqmail}.
89
3b5ba7331eb5 complete restructuring of whole document
meillo@marmaro.de
parents:
diff changeset
218
3b5ba7331eb5 complete restructuring of whole document
meillo@marmaro.de
parents:
diff changeset
219
117
098bd0876934 worked on ch03 (MTAs)
meillo@marmaro.de
parents: 116
diff changeset
220
120
3b5e6ffd7b27 typographic cleanups
meillo@marmaro.de
parents: 119
diff changeset
221 \subsubsection*{postfix}
89
3b5ba7331eb5 complete restructuring of whole document
meillo@marmaro.de
parents:
diff changeset
222 \label{sec:postfix}
391
16d8eacf60e1 created index (it is not finished)
meillo@marmaro.de
parents: 378
diff changeset
223 \index{postfix}
16d8eacf60e1 created index (it is not finished)
meillo@marmaro.de
parents: 378
diff changeset
224
377
90d5f98e3968 proof read ch03
meillo@marmaro.de
parents: 374
diff changeset
225 The \postfix\ project started in 1999 at \NAME{IBM} \name{research}, then called \name{VMailer} or \NAME{IBM} \name{Secure Mailer}. \person{Wietse Venema}'s program ``attempts to be fast, easy to administer, and secure. The outside has a definite Sendmail-ish flavor, but the inside is completely different.'' \citeweb{postfix:homepage}. In fact, \postfix\ was mainly designed after qmail's architecture to gain security. But in contrast to \qmail\ it aims much more on being fast and full-featured.
402
e57129f57faa finished the indexing in a huge last effort
meillo@marmaro.de
parents: 400
diff changeset
226 \index{qmail}
89
3b5ba7331eb5 complete restructuring of whole document
meillo@marmaro.de
parents:
diff changeset
227
394
7d85fd0da3df remove further shortcuts
meillo@marmaro.de
parents: 393
diff changeset
228 Today \postfix\ is taken by many Unix systems and \NAME{GNU}/Linux distributions as default \MTA.
402
e57129f57faa finished the indexing in a huge last effort
meillo@marmaro.de
parents: 400
diff changeset
229 \index{Unix}
89
3b5ba7331eb5 complete restructuring of whole document
meillo@marmaro.de
parents:
diff changeset
230
377
90d5f98e3968 proof read ch03
meillo@marmaro.de
parents: 374
diff changeset
231 The latest stable version is numbered 2.5.6 from December 2008. \postfix\ is covered by the \NAME{IBM} \name{Public License 1.0} which is a Free Software license.
89
3b5ba7331eb5 complete restructuring of whole document
meillo@marmaro.de
parents:
diff changeset
232
217
d645ac015c3b a lot of rework
meillo@marmaro.de
parents: 211
diff changeset
233 Additional information can be retrieved from the program's homepage \citeweb{postfix:homepage}. \person{Dent}'s \postfix\ book \cite{dent04} claims to be ``the definitive guide'', and it is.
89
3b5ba7331eb5 complete restructuring of whole document
meillo@marmaro.de
parents:
diff changeset
234
3b5ba7331eb5 complete restructuring of whole document
meillo@marmaro.de
parents:
diff changeset
235
3b5ba7331eb5 complete restructuring of whole document
meillo@marmaro.de
parents:
diff changeset
236
3b5ba7331eb5 complete restructuring of whole document
meillo@marmaro.de
parents:
diff changeset
237
3b5ba7331eb5 complete restructuring of whole document
meillo@marmaro.de
parents:
diff changeset
238
3b5ba7331eb5 complete restructuring of whole document
meillo@marmaro.de
parents:
diff changeset
239
120
3b5e6ffd7b27 typographic cleanups
meillo@marmaro.de
parents: 119
diff changeset
240 \section{Comparison of MTAs}
308
273f2d174315 small rework
meillo@marmaro.de
parents: 287
diff changeset
241 \label{sec:mta-comparison}
391
16d8eacf60e1 created index (it is not finished)
meillo@marmaro.de
parents: 378
diff changeset
242 \index{mta!comparison}
89
3b5ba7331eb5 complete restructuring of whole document
meillo@marmaro.de
parents:
diff changeset
243
312
a62fe460b8de work in MTA comparison
meillo@marmaro.de
parents: 308
diff changeset
244 This section does not try to provide a throughout \MTA\ comparison, because this is already done by others. Remarkable comparisons are the one by \person{Dan Shearer} \cite{shearer06} and a discussion on the mailing list \name{plug@lists.q-linux.com} \cite{plug:mtas}. Tabular overviews may be found at \citeweb{mailsoftware42}, \citeweb{wikipedia:comparison-of-mail-servers}, and \cite[section 1.9]{lifewithqmail}.
89
3b5ba7331eb5 complete restructuring of whole document
meillo@marmaro.de
parents:
diff changeset
245
378
c9a6cbce35fd inserted non-break spaces where appropriate
meillo@marmaro.de
parents: 377
diff changeset
246 Here provided is an overview on important properties of the four previously introduced \MTA{}s. The data comes from the above stated sources and is collected in table~\ref{tab:mta-comparison}\footnote{The lines of code were measured with \person{David~A.\ Wheeler}'s \name{sloccount} \citeweb{sloccount}.}.
402
e57129f57faa finished the indexing in a huge last effort
meillo@marmaro.de
parents: 400
diff changeset
247 \index{lines of code}
128
6f622eb5c812 some sentences about MTA comparison
meillo@marmaro.de
parents: 126
diff changeset
248
117
098bd0876934 worked on ch03 (MTAs)
meillo@marmaro.de
parents: 116
diff changeset
249 \begin{table}
126
27ddf2506157 outsourced floats; minor stuff
meillo@marmaro.de
parents: 124
diff changeset
250 \begin{center}
271
c80b6b6fb798 moved tables from input to tbl
meillo@marmaro.de
parents: 265
diff changeset
251 \input{tbl/mta-comparison.tbl}
126
27ddf2506157 outsourced floats; minor stuff
meillo@marmaro.de
parents: 124
diff changeset
252 \end{center}
312
a62fe460b8de work in MTA comparison
meillo@marmaro.de
parents: 308
diff changeset
253 \caption{Comparison of \MTA{}s}
126
27ddf2506157 outsourced floats; minor stuff
meillo@marmaro.de
parents: 124
diff changeset
254 \label{tab:mta-comparison}
117
098bd0876934 worked on ch03 (MTAs)
meillo@marmaro.de
parents: 116
diff changeset
255 \end{table}
89
3b5ba7331eb5 complete restructuring of whole document
meillo@marmaro.de
parents:
diff changeset
256
3b5ba7331eb5 complete restructuring of whole document
meillo@marmaro.de
parents:
diff changeset
257
201
013a13ee0a5f subsections to unnumbered subsubsections
meillo@marmaro.de
parents: 193
diff changeset
258 \subsubsection*{Architecture}
391
16d8eacf60e1 created index (it is not finished)
meillo@marmaro.de
parents: 378
diff changeset
259 \index{mta!architecture}
126
27ddf2506157 outsourced floats; minor stuff
meillo@marmaro.de
parents: 124
diff changeset
260
392
b4611d4e1484 applied comments by henry atting
meillo@marmaro.de
parents: 391
diff changeset
261 Architecture is most important when comparing \MTA{}s. Many other properties of a program depend on its architecture. \person{Munawar Hafiz} discusses in detail on \MTA\ architecture, comparing \sendmail, \qmail, \postfix, and \name{sendmail~X} \cite{hafiz05}. \person{Jonathan de Boyne Pollard}'s \MTA\ review \cite{jdebp} is a source, too.
126
27ddf2506157 outsourced floats; minor stuff
meillo@marmaro.de
parents: 124
diff changeset
262
373
d51894e48762 started indexing; mta -> MTA (many small changes)
meillo@marmaro.de
parents: 364
diff changeset
263 Two different architecture types show off: monolithic and modular \MTA{}s.
126
27ddf2506157 outsourced floats; minor stuff
meillo@marmaro.de
parents: 124
diff changeset
264
377
90d5f98e3968 proof read ch03
meillo@marmaro.de
parents: 374
diff changeset
265 Monolithic \MTA{}s are \sendmail, \name{smail}, \exim, and \masqmail. They all consist of one single \emph{setuid root}\footnote{\emph{setuid} lets a program run with the rights of its owner, here root. This is considered to be a security risk. Thus it it should be avoided if possible.} binary which does all the work.
402
e57129f57faa finished the indexing in a huge last effort
meillo@marmaro.de
parents: 400
diff changeset
266 \index{root privilege}
e57129f57faa finished the indexing in a huge last effort
meillo@marmaro.de
parents: 400
diff changeset
267 \index{setuid}
e57129f57faa finished the indexing in a huge last effort
meillo@marmaro.de
parents: 400
diff changeset
268 \index{sendmail}
e57129f57faa finished the indexing in a huge last effort
meillo@marmaro.de
parents: 400
diff changeset
269 \index{exim}
e57129f57faa finished the indexing in a huge last effort
meillo@marmaro.de
parents: 400
diff changeset
270 \index{smail}
126
27ddf2506157 outsourced floats; minor stuff
meillo@marmaro.de
parents: 124
diff changeset
271
377
90d5f98e3968 proof read ch03
meillo@marmaro.de
parents: 374
diff changeset
272 Modular \MTA{}s are \NAME{MMDF}, \qmail, \postfix, and \name{MeTA1}. They consist of several programs, each doing only a part of the overall job. The different programs run with the least permissions they need, \emph{setuid root} can be avoided completely.
402
e57129f57faa finished the indexing in a huge last effort
meillo@marmaro.de
parents: 400
diff changeset
273 \index{postfix}
e57129f57faa finished the indexing in a huge last effort
meillo@marmaro.de
parents: 400
diff changeset
274 \index{qmail}
e57129f57faa finished the indexing in a huge last effort
meillo@marmaro.de
parents: 400
diff changeset
275 \index{mmdf}
e57129f57faa finished the indexing in a huge last effort
meillo@marmaro.de
parents: 400
diff changeset
276 \index{sendmail!meta1}
89
3b5ba7331eb5 complete restructuring of whole document
meillo@marmaro.de
parents:
diff changeset
277
378
c9a6cbce35fd inserted non-break spaces where appropriate
meillo@marmaro.de
parents: 377
diff changeset
278 The architecture does not directly define the program's security, but ``[t]he goal of making a software secure can be better achieved by making the design simple and easier to understand and verify'' \cite[chapter~6]{hafiz05}. \exim, though being monolithic, has a fairly clean security record. But it is very hard to keep the security up as the program growth. \person{Wietse Venema} (the author of \postfix) says, it was the architecture that enabled \postfix\ to grow without running into security problems \cite[page 13]{venema:postfix-growth}.
391
16d8eacf60e1 created index (it is not finished)
meillo@marmaro.de
parents: 378
diff changeset
279 \index{security}
402
e57129f57faa finished the indexing in a huge last effort
meillo@marmaro.de
parents: 400
diff changeset
280 \index{postfix}
e57129f57faa finished the indexing in a huge last effort
meillo@marmaro.de
parents: 400
diff changeset
281 \index{exim}
89
3b5ba7331eb5 complete restructuring of whole document
meillo@marmaro.de
parents:
diff changeset
282
217
d645ac015c3b a lot of rework
meillo@marmaro.de
parents: 211
diff changeset
283 The modular design, with each sub-program doing one part of the overall job, conforms to the \name{Unix Philosophy}. The Unix Philosophy \cite{gancarz95} demands ``small is beautiful'' and ``make each program do one thing well''. Monolithic \MTA{}s fail here.
402
e57129f57faa finished the indexing in a huge last effort
meillo@marmaro.de
parents: 400
diff changeset
284 \index{Unix!philosophy}
89
3b5ba7331eb5 complete restructuring of whole document
meillo@marmaro.de
parents:
diff changeset
285
373
d51894e48762 started indexing; mta -> MTA (many small changes)
meillo@marmaro.de
parents: 364
diff changeset
286 Today modular \MTA\ architectures are the state-of-the-art.
89
3b5ba7331eb5 complete restructuring of whole document
meillo@marmaro.de
parents:
diff changeset
287
3b5ba7331eb5 complete restructuring of whole document
meillo@marmaro.de
parents:
diff changeset
288
217
d645ac015c3b a lot of rework
meillo@marmaro.de
parents: 211
diff changeset
289 \subsubsection*{Spam checking and content processing}
391
16d8eacf60e1 created index (it is not finished)
meillo@marmaro.de
parents: 378
diff changeset
290 \index{spam}
89
3b5ba7331eb5 complete restructuring of whole document
meillo@marmaro.de
parents:
diff changeset
291
377
90d5f98e3968 proof read ch03
meillo@marmaro.de
parents: 374
diff changeset
292 Spam and malware increased during the last years. Today it is important for an \MTA\ to be able to provide checking for bad mail. This can be done by implementing functionality into the \MTA\ or by invoking external programs to do this job.
313
a3fba017ef01 added missing parts to ch03
meillo@marmaro.de
parents: 312
diff changeset
293
377
90d5f98e3968 proof read ch03
meillo@marmaro.de
parents: 374
diff changeset
294 \sendmail\ invented \name{milter}\footnote{``milter'' is a common abbreviation for ``sendmail mail filter \NAME{API}''.}, which is used to interface external programs of various kind. \postfix\ adopted the \name{milter} interface but is also able to easily include scanning modules into its modular structure. \qmail\ is pretty old and did not evolve with the changing market situation. Anyhow, its modular structure enables external scanners to be included into \qmail. \exim\ has the advantage that it was designed with the goal to provide extensive scanning facilities; it is therefore very good suited to scan itself or invoke external scanners.
402
e57129f57faa finished the indexing in a huge last effort
meillo@marmaro.de
parents: 400
diff changeset
295 \index{sendmail}
e57129f57faa finished the indexing in a huge last effort
meillo@marmaro.de
parents: 400
diff changeset
296 \index{postfix}
e57129f57faa finished the indexing in a huge last effort
meillo@marmaro.de
parents: 400
diff changeset
297 \index{qmail}
391
16d8eacf60e1 created index (it is not finished)
meillo@marmaro.de
parents: 378
diff changeset
298 \index{milter}
402
e57129f57faa finished the indexing in a huge last effort
meillo@marmaro.de
parents: 400
diff changeset
299 \index{exim}
126
27ddf2506157 outsourced floats; minor stuff
meillo@marmaro.de
parents: 124
diff changeset
300
217
d645ac015c3b a lot of rework
meillo@marmaro.de
parents: 211
diff changeset
301
377
90d5f98e3968 proof read ch03
meillo@marmaro.de
parents: 374
diff changeset
302 \subsubsection*{Future trends}
126
27ddf2506157 outsourced floats; minor stuff
meillo@marmaro.de
parents: 124
diff changeset
303
378
c9a6cbce35fd inserted non-break spaces where appropriate
meillo@marmaro.de
parents: 377
diff changeset
304 In chapter~\ref{chap:market-analysis}, it was tried to figure out trends and future requirements for \MTA{}s. The four programs are compared on these possible future requirements now.
391
16d8eacf60e1 created index (it is not finished)
meillo@marmaro.de
parents: 378
diff changeset
305 \index{email!trends}
313
a3fba017ef01 added missing parts to ch03
meillo@marmaro.de
parents: 312
diff changeset
306
377
90d5f98e3968 proof read ch03
meillo@marmaro.de
parents: 374
diff changeset
307 \paragraph{Provider independence}
90d5f98e3968 proof read ch03
meillo@marmaro.de
parents: 374
diff changeset
308 The first trend was provider independence, which requires easy configuration. \postfix\ seems to do best here. It uses primary two configuration files (\path{master.cf} and \path{main.cf}) which are easy to manage. \sendmail\ appears to have a bad position. Its configuration file \path{sendmail.cf} is cryptic and very complex (it has legendary Turing-completeness) thus it needs simplification wrappers around it to provide easier configuration. They exist in form of the \name{m4} macros that generate the \path{sendmail.cf} file. Unfortunately, adjusting the generated result by hand appears to be necessary for non-trivial configurations. \qmail's configuration files are simple but the whole system is complex to set up; it requires various system users and \qmail\ is hardly usable without applying several patches that add functionality which is required nowadays. \name{netqmail} is the community's effort to help in the latter point. \exim\ has only one single configuration file (\path{exim.conf}) which suffers most from its flexibility---like in \sendmail's case. Flexibility and easy configuration are almost always contrary goals.
402
e57129f57faa finished the indexing in a huge last effort
meillo@marmaro.de
parents: 400
diff changeset
309 \index{sendmail}
e57129f57faa finished the indexing in a huge last effort
meillo@marmaro.de
parents: 400
diff changeset
310 \index{postfix}
e57129f57faa finished the indexing in a huge last effort
meillo@marmaro.de
parents: 400
diff changeset
311 \index{qmail}
e57129f57faa finished the indexing in a huge last effort
meillo@marmaro.de
parents: 400
diff changeset
312 \index{wrapper}
e57129f57faa finished the indexing in a huge last effort
meillo@marmaro.de
parents: 400
diff changeset
313 \index{exim}
e57129f57faa finished the indexing in a huge last effort
meillo@marmaro.de
parents: 400
diff changeset
314 \index{configuration}
e57129f57faa finished the indexing in a huge last effort
meillo@marmaro.de
parents: 400
diff changeset
315 \index{m4 macros}
313
a3fba017ef01 added missing parts to ch03
meillo@marmaro.de
parents: 312
diff changeset
316
377
90d5f98e3968 proof read ch03
meillo@marmaro.de
parents: 374
diff changeset
317 \paragraph{Performance}
391
16d8eacf60e1 created index (it is not finished)
meillo@marmaro.de
parents: 378
diff changeset
318 \index{performance}
400
5254a119ad56 fixed all major trashing of the right margin
meillo@marmaro.de
parents: 396
diff changeset
319 As second trend was the decreasing necessity for high per\-for\-mance identified. This goes along with the move of \MTA{}s from service providers to home servers. \postfix\ focuses much on performance, this might not be an important point in the future. Of course there will still be the need for high performance \MTA{}s, but a growing share of the market will not require high performance. Energy and space efficiency is related to performance; it is a similar goal in a different direction. But optimization, be it for performance or other efficiencies, is often in contrast to simplicity and clarity; these two improve security. Optimizing does in most times decrease the simplicity and clarity. Simple \MTA{}s that do not aim for high performance are what is needed in future. The simple design of \qmail\footnote{\qmail\ is still fast} is a good example.
402
e57129f57faa finished the indexing in a huge last effort
meillo@marmaro.de
parents: 400
diff changeset
320 \index{postfix}
e57129f57faa finished the indexing in a huge last effort
meillo@marmaro.de
parents: 400
diff changeset
321 \index{qmail}
93
a6f8a93abd64 new chapter 4 (split ch5); added lots of annotations
meillo@marmaro.de
parents: 92
diff changeset
322
377
90d5f98e3968 proof read ch03
meillo@marmaro.de
parents: 374
diff changeset
323 \paragraph{Security}
391
16d8eacf60e1 created index (it is not finished)
meillo@marmaro.de
parents: 378
diff changeset
324 \index{security}
392
b4611d4e1484 applied comments by henry atting
meillo@marmaro.de
parents: 391
diff changeset
325 The third trend (even more security awareness) is addressed by each of the four programs. It seems as if all widely used \MTA{}s provide good security nowadays. Even \sendmail\ can be configured to be secure today. However, the modular architecture, used by \qmail\ and \postfix, is generally seen to be conceptually more secure. \sendmail's creators have started \name{MeTA1}, a modular \MTA\ that merges the best of \qmail\ and \postfix, to replace the old \sendmail. It will be interesting to watch \exim's future---will it become modular, too?
402
e57129f57faa finished the indexing in a huge last effort
meillo@marmaro.de
parents: 400
diff changeset
326 \index{sendmail}
e57129f57faa finished the indexing in a huge last effort
meillo@marmaro.de
parents: 400
diff changeset
327 \index{postfix}
e57129f57faa finished the indexing in a huge last effort
meillo@marmaro.de
parents: 400
diff changeset
328 \index{qmail}
e57129f57faa finished the indexing in a huge last effort
meillo@marmaro.de
parents: 400
diff changeset
329 \index{sendmail!meta1}
e57129f57faa finished the indexing in a huge last effort
meillo@marmaro.de
parents: 400
diff changeset
330 \index{exim}
89
3b5ba7331eb5 complete restructuring of whole document
meillo@marmaro.de
parents:
diff changeset
331
117
098bd0876934 worked on ch03 (MTAs)
meillo@marmaro.de
parents: 116
diff changeset
332
130
6ce355da579f market share stuff and more
meillo@marmaro.de
parents: 128
diff changeset
333
265
6ed93483bba9 added section about masqmails position
meillo@marmaro.de
parents: 259
diff changeset
334
6ed93483bba9 added section about masqmails position
meillo@marmaro.de
parents: 259
diff changeset
335
6ed93483bba9 added section about masqmails position
meillo@marmaro.de
parents: 259
diff changeset
336
287
6cf649e62d42 minor renames and commenting
meillo@marmaro.de
parents: 276
diff changeset
337 \section{Summary}
193
ee687abf386c a result is needed here
meillo@marmaro.de
parents: 155
diff changeset
338
313
a3fba017ef01 added missing parts to ch03
meillo@marmaro.de
parents: 312
diff changeset
339 This chapter first took an overview over the field of \MTA{}s. Three major types of \MTA{}s were identified: Relay-only \MTA{}s (also called forwarders), groupware, and the ``real \MTA{}s''. \masqmail\ belongs to the last group, it is additionally sendmail-compatible and Free Software.
a3fba017ef01 added missing parts to ch03
meillo@marmaro.de
parents: 312
diff changeset
340
377
90d5f98e3968 proof read ch03
meillo@marmaro.de
parents: 374
diff changeset
341 Next a look at the market shares of \MTA{}s was taken; It showed that four \MTA{}s of \masqmail's group have high importance: \sendmail, \postfix, \qmail, and \exim. Their combined share is between one third and the half of the market. The other part splits into proprietary \MTA{}s, unknown software behind mail security layers, and a reminder of really small market shares.
276
ce4d5b39e554 marked a missing part
meillo@marmaro.de
parents: 271
diff changeset
342
377
90d5f98e3968 proof read ch03
meillo@marmaro.de
parents: 374
diff changeset
343 Each one of the four major Free Software \MTA{}s was presented afterwards and finally these programs were compared on some selected properties.
130
6ce355da579f market share stuff and more
meillo@marmaro.de
parents: 128
diff changeset
344
377
90d5f98e3968 proof read ch03
meillo@marmaro.de
parents: 374
diff changeset
345 Now, the reader should have a general knowledge about those four important \MTA{}s. Further chapters will refer frequently to them.
117
098bd0876934 worked on ch03 (MTAs)
meillo@marmaro.de
parents: 116
diff changeset
346
098bd0876934 worked on ch03 (MTAs)
meillo@marmaro.de
parents: 116
diff changeset
347