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comparison thesis/tex/3-MailTransferAgents.tex @ 225:47af8eb539cf proof-read version for ben and james (ch234)

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author meillo@marmaro.de
date Tue, 06 Jan 2009 18:04:18 +0100
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87 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 \freesw\ \mta{}s (\name{smail}, \name{zmailer}, \name{MMDF}, \name{courier-mta}) are less important and seldom used. 87 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 \freesw\ \mta{}s (\name{smail}, \name{zmailer}, \name{MMDF}, \name{courier-mta}) are less important and seldom used.
88 88
89 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 \person{Simpson} and \person{Bekman} 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. 89 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 \person{Simpson} and \person{Bekman} 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.
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91 All surveys show \sendmail\ to be the most popular \MTA. \postfix, \qmail, and \exim\ are among the best seven in each. \exim\ has slightly smaller shares than the other two. The four together share more than half of the market according to \person{Bernstein} and the \name{MailRadar} statistics. \person{Simpson} and \person{Bekman} have their share to be somewhere between a third and the half. This uncertainty comes from the large amount of unidentifieable \MTA{}s. 91 All surveys show \sendmail\ to be the most popular \MTA. \postfix, \qmail, and \exim\ are among the best seven in each. \exim\ has slightly smaller shares than the other two. The four together share more than half of the market according to \person{Bernstein} and the \name{MailRadar} statistics. \person{Simpson} and \person{Bekman} have their share to be somewhere between a third and the half. This uncertainty comes from the large amount of unidentifiable \MTA{}s.
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93 The 22 percent of \name{mail security layers} in the \name{O'Reilly} 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. This large share may be a result of only regarding business mail servers. The problem concerning the survey is the deguise of the \mta\ working 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 using the \name{O'Reilly} survey. 93 The 22 percent of \name{mail security layers} in the \name{O'Reilly} 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. This large share may be a result of only regarding business mail servers. The problem concerning the survey is the disguise of the \mta\ working 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 using the \name{O'Reilly} survey.
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95 The date of the \name{Mailradar} statistics ist not mentioned with it; a mail to \name{Mailradar} asking for information was not 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'Reilly} would be just guessing. 95 The date of the \name{Mailradar} statistics is not mentioned with it; a mail to \name{Mailradar} asking for information was not 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'Reilly} would be just guessing.
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98 \subsection{The four major Free Software MTAs} 98 \subsection{The four major Free Software MTAs}
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100 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 Jonathan \person{de Boyne Pollard} \cite{jdebp}. 100 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 Jonathan \person{de Boyne Pollard} \cite{jdebp}.
133 \label{sec:qmail} 133 \label{sec:qmail}
134 \qmail\ is seen by its community as ``a modern SMTP server which makes sendmail obsolete'' \citeweb{qmail:homepage2}. It was written by Daniel~J.\ \person{Bernstein} starting in 1995. His primary goal was to create a secure \MTA\ to replace the popular, but vulnerable, \sendmail. %fixme: ref 134 \qmail\ is seen by its community as ``a modern SMTP server which makes sendmail obsolete'' \citeweb{qmail:homepage2}. It was written by Daniel~J.\ \person{Bernstein} starting in 1995. His primary goal was to create a secure \MTA\ to replace the popular, but vulnerable, \sendmail. %fixme: ref
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136 \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. %fixme:ref 136 \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. %fixme:ref
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138 The latest release of \qmail\ is versoin 1.03 from July 1998. In November 2007, afterwards, \qmail's source was put into the \name{public domain}. This makes it Free Software. 138 The latest release of \qmail\ is version 1.03 from July 1998. In November 2007, afterwards, \qmail's source was put into the \name{public domain}. This makes it Free Software.
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140 Because of \person{Bernstein}'s inactivity though changing requirements since 1998, ``[a] motley krewe of qmail contributors (see the 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}. 140 Because of \person{Bernstein}'s inactivity though changing requirements since 1998, ``[a] motley krewe of qmail contributors (see the 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}.
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142 \qmail's homepages are \citeweb{qmail:homepage1} and \citeweb{qmail:homepage2}. The best book about \qmail, from \person{Bernstein}'s view, is Dave \person{Sill}'s handbook \cite{sill02}. His free available guide ``Life with qmail'' is another valuable source \cite{lifewithqmail}. 142 \qmail's homepages are \citeweb{qmail:homepage1} and \citeweb{qmail:homepage2}. The best book about \qmail, from \person{Bernstein}'s view, is Dave \person{Sill}'s handbook \cite{sill02}. His free available guide ``Life with qmail'' is another valuable source \cite{lifewithqmail}.
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161 \section{Comparison of MTAs} 161 \section{Comparison of MTAs}
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163 This section does not try to provide an overall \MTA\ comparison, because this is already done by others. Remarkable comparisons are the one by Dan \person{Shearer} \cite{shearer06} and a discussion on the mailing list \name{plug@lists.q-linux.com} \cite{plug:mtas}. Tabulary overviews may be found at \citeweb{mailsoftware42}, \citeweb{wikipedia:comparison-of-mail-servers}, and \cite[section 1.9]{lifewithqmail}. 163 This section does not try to provide an overall \MTA\ comparison, because this is already done by others. Remarkable comparisons are the one by Dan \person{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}.
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165 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}. 165 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}.
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167 \begin{table} 167 \begin{table}
168 % FIXME: improve table data!!! 168 % FIXME: improve table data!!!
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200 \subsubsection*{Future requirements} 200 \subsubsection*{Future requirements}
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202 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. 202 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.
203 203
204 The first trend was provider independence, requiring easy configuration. \postfix\ seems to do best here. It used 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. There exist the \name{m4} macros to generate \path{sendmail.cf}, but adjusting the generated result by hand appears to be nessesary 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 is hardly usable without applying several patches to add basic functionality. \name{netqmail} is the community effort to help here. \exim\ has only one single configuration file (\path{exim.conf}), but it suffers most from its flexibility---like \sendmail. Flexibility and easy configuration are almost always contrary goals. 204 The first trend was provider independence, requiring easy configuration. \postfix\ seems to do best here. It used 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. There exist the \name{m4} macros to generate \path{sendmail.cf}, but 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 is hardly usable without applying several patches to add basic functionality. \name{netqmail} is the community effort to help here. \exim\ has only one single configuration file (\path{exim.conf}), but it suffers most from its flexibility---like \sendmail. Flexibility and easy configuration are almost always contrary goals.
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206 As second trend, the decreasing nessesarity for high performance was 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 then. Of course there still will be the need for high performance \MTA{}s, but a growing share of the market will not require high performance. Performance is related to simplicity, which effects security. Increasing performance does in most times decrease the other two. Simple \mta{}s not aiming for highest performance are what is needed in future. The simple of \qmail, still being fast, seems to be a good example. 206 As second trend, the decreasing necessity for high performance was 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 then. Of course there still will be the need for high performance \MTA{}s, but a growing share of the market will not require high performance. Performance is related to simplicity, which effects security. Increasing performance does in most times decrease the other two. Simple \mta{}s not aiming for highest performance are what is needed in future. The simple of \qmail, still being fast, seems to be a good example.
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208 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 considered secure today. %fixme:ref 208 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 considered secure today. %fixme:ref
209 But the modular architecture, used by \qmail\ and \postfix, is generally seen to be conceptually more secure, however. %fixme: ref 209 But the modular architecture, used by \qmail\ and \postfix, is generally seen to be conceptually more secure, however. %fixme: ref
210 \sendmail's creators have started \name{MeTA1}, a modular \MTA\ merging 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? 210 \sendmail's creators have started \name{MeTA1}, a modular \MTA\ merging 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?
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