1.1 --- a/thesis/tex/3-MailTransferAgents.tex	Wed Dec 10 08:32:12 2008 +0100
     1.2 +++ b/thesis/tex/3-MailTransferAgents.tex	Wed Dec 10 16:48:41 2008 +0100
     1.3 @@ -8,7 +8,7 @@
     1.4  \section{Types of MTAs}
     1.5  ``Mail transfer agent'' is a term covering a variety of programs. One thing is common to them: they transfer email from one machine to another.
     1.6  
     1.7 -This is how Bryan Costales defines a \mta\ in \cite{costales97}:
     1.8 +This is how \person{Bryan Costales} defines a \mta\ in \cite{costales97}:
     1.9  \begin{quote}
    1.10  A mail transfer agent (MTA) is a highly specialized program that delivers mail and transports it between machines, like the post office.
    1.11  \end{quote}
    1.12 @@ -44,7 +44,7 @@
    1.13  \subsubsection*{``Real'' MTAs}
    1.14  There is a third type of \mta{}s in between the minimalistic \name{relay-only} \MTA{}s and the bloated \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 ``\mta''---programs that transfer mail between hosts.
    1.15  
    1.16 -Common to them is their focus on transferring email, while being able to act as \name{smart host}. Their variety ranges from ones mostly restricted to mail transfer (\name{qmail}) to others already having interfaces for adding further mail processing modules (\name{postfix}). They cover everything in between the other two groups.  %FIXME: are postfix and qmail good examples?
    1.17 +Common to them is their focus on transferring email, while being able to act as \name{smart host}. Their variety ranges from ones mostly restricted to mail transfer (\qmail) to others already having interfaces for adding further mail processing modules (\postfix). They cover everything in between the other two groups.  %FIXME: are postfix and qmail good examples?
    1.18  
    1.19  This group is of importance in this document. All programs selected for the comparison in the following section are ``real \MTA{}s''. \masqmail\ is one too.
    1.20  
    1.21 @@ -69,9 +69,9 @@
    1.22  
    1.23  This section introduces a selection of popular \MTA{}s; they are the most likely substitutes for \masqmail. All are \emph{sendmail-compatible} ``smart'' \freesw\ \MTA{}s that focus on mail transfer, as is \masqmail.
    1.24  
    1.25 -The programs chosen are: \sendmail, \name{exim}, \name{qmail}, and \name{postfix}. They are the most important representatives of the regarded group. Although \MTA\ statistics are rare, FIXME(have different results), and good data is hard to collect, these programs tend to stay near the top.
    1.26 +The programs chosen are: \sendmail, \exim, \qmail, and \postfix. They are the most important representatives of the regarded group. Although \MTA\ statistics are rare, FIXME(have different results), and good data is hard to collect, these programs tend to stay near the top.
    1.27  
    1.28 -Table \ref{tab:mta-market-share} shows the Top 10 \MTA{}s of three different statistics. The first published by \name{O'ReillyNet} in YYYY \citeweb{oreillynet:mta-stats} , the second by \name{Mailradar.com} from YYYY \citeweb{mailradar:mta-stats} , and the third by \textsc{Daniel~J.\ Bernstein} (the author of \name{qmail}) done in 2001 \citeweb{djb:mta-stats}.
    1.29 +Table \ref{tab:mta-market-share} shows the Top 10 \MTA{}s of three different statistics. The first published by \name{O'ReillyNet} in YYYY \citeweb{oreillynet:mta-stats} , the second by \name{Mailradar.com} from YYYY \citeweb{mailradar:mta-stats} , and the third by \person{Daniel~J.\ Bernstein} (the author of \qmail) done in 2001 \citeweb{djb:mta-stats}.
    1.30  
    1.31  \begin{table}
    1.32  	\begin{center}
    1.33 @@ -81,10 +81,10 @@
    1.34  	\label{tab:mta-market-share}
    1.35  \end{table}
    1.36  
    1.37 -Other members of the same group are: \name{smail}, \name{zmailer}, \name{mmdf}, and \name{courier-mta}. They all are less important and rarely used, thus ommited here.
    1.38 +Other members of the same group are: \name{smail}, \name{zmailer}, \name{MMDF}, and \name{courier-mta}. They all are less important and rarely used, thus ommited here.
    1.39  
    1.40  
    1.41 -Now follows a small introduction to the five programs chosen for comparison, except \masqmail\ which already was introduced in chapter \ref{chap:introduction}. Longer introductions, including analysis and comparison, were written by \textsc{Jonathan de Boyne Pollard} \citeweb{jdebp}.
    1.42 +Now follows a small introduction to the five programs chosen for comparison, except \masqmail\ which already was introduced in chapter \ref{chap:introduction}. Longer introductions, including analysis and comparison, were written by \person{Jonathan de Boyne Pollard} \citeweb{jdebp}.
    1.43  
    1.44  
    1.45  
    1.46 @@ -92,7 +92,7 @@
    1.47  \label{sec:sendmail}
    1.48  \sendmail\ is the most popular \mta, since it was one of the first and was shipped as default \MTA{}s by many vendors of \unix\ systems. %fixme: ref
    1.49  
    1.50 -The program was written by Eric Allman as the successor of his program \name{delivermail}. \sendmail\ was first released with \NAME{BSD} 4.1c in 1983. Allman was not the only one 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. %fixme: ref
    1.51 +The program was written by \person{Eric Allman} as the successor of his program \name{delivermail}. \sendmail\ was first released with \NAME{BSD} 4.1c in 1983. Allman was not the only one 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. %fixme: ref
    1.52  
    1.53  \sendmail\ is focused on transferring mails between different protocols and networks, this lead to a very flexible (though complex) configuration.
    1.54  
    1.55 @@ -106,39 +106,39 @@
    1.56  
    1.57  \subsubsection*{exim}
    1.58  \label{sec:exim}
    1.59 -\name{exim} was started in 1995 by Philip Hazel at the \name{University of Cambridge}. It is forked of \name{smail-3}, and inherited the monolithic architecture, similar to \sendmail's. But having no separation of the individual components of the system, like \name{qmail} and \name{postfix} have, did not hurt. Its security is comparably good. %fixme: ref
    1.60 +\exim\ was started in 1995 by \person{Philip Hazel} at the \name{University of Cambridge}. It is forked of \name{smail-3}, and inherited the monolithic architecture, similar to \sendmail's. But having no separation of the individual components of the system, like \qmail\ and \postfix\ have, did not hurt. Its security is comparably good. %fixme: ref
    1.61  
    1.62 -\name{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. Also interfaces for integration of virus and spam check programs are provided by design. %fixme: ref
    1.63 +\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. Also interfaces for integration of virus and spam check programs are provided by design. %fixme: ref
    1.64  
    1.65  The program is \freesw, released under the \GPL. The latest stable version is 4.69 from December 2007.
    1.66  
    1.67 -One finds \name{exim} on its homepage \citeweb{exim:homepage}.
    1.68 +One finds \exim\ on its homepage \citeweb{exim:homepage}.
    1.69  
    1.70  
    1.71  
    1.72  \subsubsection*{qmail}
    1.73  \label{sec:qmail}
    1.74 -\name{qmail} is seen by its community as ``a modern SMTP server which makes sendmail obsolete''.%fixme: ref
    1.75 -It was written by Daniel~J.\ Bernstein starting in 1995. His primary goal was to create a secure \MTA\ to replace the popular, but vulnerable, \sendmail. %fixme: ref
    1.76 +\qmail\ is seen by its community as ``a modern SMTP server which makes sendmail obsolete''.%fixme: ref
    1.77 +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. %fixme: ref
    1.78  
    1.79 -\name{qmail} first introduced many innovative concepts in \mta\ design and is generally seen as the first security-aware \MTA\ developed. %fixme:ref
    1.80 +\qmail\ first introduced many innovative concepts in \mta\ design and is generally seen as the first security-aware \MTA\ developed. %fixme:ref
    1.81  %fixme: what about mmdf?
    1.82  
    1.83 -Since November 2007, \name{qmail} is released in the \name{public domain} which makes it \freesw. The latest release is 1.03 from July 1998.
    1.84 +Since November 2007, \qmail\ is released in the \name{public domain} which makes it \freesw. The latest release is 1.03 from July 1998.
    1.85  
    1.86 -The programs homepages are \citeweb{qmail:homepage1} and \citeweb{qmail:homepage2}. Further information about \name{qmail} is available with Dave Sill's ``Life with qmail'' \citeweb{lifewithqmail}.
    1.87 +The programs homepages are \citeweb{qmail:homepage1} and \citeweb{qmail:homepage2}. Further information about \qmail\ is available with \person{Dave Sill}'s ``Life with qmail'' \citeweb{lifewithqmail}.
    1.88  
    1.89  
    1.90  
    1.91  \subsubsection*{postfix}
    1.92  \label{sec:postfix}
    1.93 -The \name{postfix} project was started in 1999 at \name{IBM research}, then called \name{VMailer} or \name{IBM Secure Mailer}. 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, \name{postfix} was mainly designed after qmail's architecture to gain security. But in contrast to \name{qmail} it aims much more on being fast and full-featured.
    1.94 +The \postfix\ project was started in 1999 at \name{IBM research}, then called \name{VMailer} or \name{IBM 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.
    1.95  
    1.96 -Today \name{postfix} is taken by many \unix\ systems and \gnulinux\ distributions as default \MTA.
    1.97 +Today \postfix\ is taken by many \unix\ systems and \gnulinux\ distributions as default \MTA.
    1.98  
    1.99 -The latest stable version is numbered 2.5.5 from August 2008. \name{postfix} is covered by the \name{IBM Public License 1.0} which is a \freesw\ license.
   1.100 +The latest stable version is numbered 2.5.5 from August 2008. \postfix\ is covered by the \name{IBM Public License 1.0} which is a \freesw\ license.
   1.101  
   1.102 -Additional information is available on the program's homepage \citeweb{postfix:homepage}.
   1.103 +Additional information can be retrieved from the program's homepage \citeweb{postfix:homepage}.
   1.104  
   1.105  
   1.106  
   1.107 @@ -147,12 +147,10 @@
   1.108  
   1.109  \section{Comparison of MTAs}
   1.110  
   1.111 -This section tries not to provide an overall \MTA\ comparison, because this is already done by others. Remarkable are the one by Shearer \cite{shearer06} and an email discussion on the mailing list \name{plug@lists.q-linux.com} \citeweb{plug:mtas}. Tabulary overviews may be found at \citeweb{mailsoftware42} and \citeweb{wikipedia:comparison-of-mail-servers}.
   1.112 +This section does not try to provide an overall \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} \citeweb{plug:mtas}. Tabulary overviews may be found at \citeweb{mailsoftware42}, \citeweb{wikipedia:comparison-of-mail-servers}, and \citeweb[section 1.9]{lifewithqmail}.
   1.113  
   1.114  Here provided is an overview on a selection of important properties, covering the four previously introduced programs. The data comes from the above stated sources and is collected in table \ref{tab:mta-comparison}.
   1.115  
   1.116 -
   1.117 -
   1.118  \begin{table}
   1.119  	\begin{center}
   1.120  		\input{input/mta-comparison.tex}
   1.121 @@ -162,51 +160,48 @@
   1.122  \end{table}
   1.123  
   1.124  
   1.125 +\subsection{Architecture}
   1.126  
   1.127 -\subsection{About architecture}
   1.128 +Architecture is most important when comparing \MTA{}s. Many other properties of a program depend on its architecture. %fixme: add ref?
   1.129 +\person{Munawar Hafiz} \cite{hafiz05} discusses in detail on \mta\ architecture, comparing \sendmail, \qmail, \postfix, and \name{sendmail X}. \person{Jonathan de Boyne Pollard}'s \MTA\ review \citeweb{jdebp} is a source too.
   1.130  
   1.131 -Hafiz \cite{hafiz05} discusses in detail on \mta\ architecture (comparing \sendmail, \name{qmail}, \name{postfix}, and \name{sendmail X}).
   1.132 +Two different architecture types show off: monolithic and modular \mta{}s.
   1.133  
   1.134 +Monolithic \MTA{}s are \sendmail, \name{smail}, \exim, and \masqmail. They all consist of one single \emph{setuid root}\footnote{\emph{setuid root} lets a program run with the rights of its owner, here root. This is considered a security risk.} binary which does all the work.
   1.135  
   1.136 -\url{http://archives.neohapsis.com/archives/postfix/2006-07/1762.html} %sloc evolution of postfix, sendmail, qmail
   1.137 +Modular \MTA{}s are \NAME{MMDF}, \qmail, \postfix, and \name{MeTA1}. They consist of several programs, each doing a part of the overall job. The different programs run with the least permissions the need, and \emph{setuid root} needs not to be used.
   1.138  
   1.139 +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. It, however, takes more effort and makes it very hard to keep the security up, as the program growth. \person{Wietse Venema} (the author of \postfix) sees in modularity the FIXME(vorraussetzung) to let \postfix\ grow without running into security problems. \citeweb{venema:postfix-growth}
   1.140  
   1.141 +The modular design, with each sub-program doing one part of the overall job, is applied \name{Unix Philosophy}. The Unix Philosophy \cite{gancarz} demands ``small is beautiful'' and ``do one job and do it good''. Monolithic \MTA{}s fail here. %fixme: check correct wording
   1.142  
   1.143 -\subsection{Security comparison}
   1.144 +Today modular \mta\ architectures are the state-of-the-art.
   1.145  
   1.146  
   1.147  
   1.148 +\subsection{With focus on the future}
   1.149  
   1.150 +Section \ref{sec:what-will-be-important} tried to figure out the importances for future \MTA{}s. The four programs are compared on these (possible) future requirements now.
   1.151  
   1.152 +The first trend was provider independence, requiring easy configuration. \postfix\ seems to do best here. It has one single configuration file (FIXME) which is easy to manage. \sendmail\ and \qmail\ appear to have bad positions. Their configuration is complex, thus they would need simplification wrappers around them to provide easy configuration. For \path{sendmail.cf} exist the \name{m4} macros, but adjusting \path{sendmail.cf} by hand seems to be nessesary for non-trivial configurations. And \path{sendmail.cf}'s complexity, including Turing-completeness,%fixme: ref
   1.153 + is legendary. \qmail's configuration files are not so complex, but the whole system (requiring various system users) is complex to set up. \exim\ suffers most from its flexibility, like \sendmail. Flexibility and easy configuration are contrary.
   1.154  
   1.155 -\paragraph{Ref back to \ref{sec:what-will-be-important}}
   1.156 +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 enough, seems to be a good example.
   1.157  
   1.158 -provider indepencence -> easy config:
   1.159 -\sendmail\ and \name{qmail} appear to have bad positions at this point. Their configuration is complex, thus they would need simplification wrappers around them to provide easy configuration.
   1.160 +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
   1.161 +The modular architecture, used by \qmail\ and \postfix, is generally seen to be conceptually more secure, however.%fixme: ref
   1.162 +\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?
   1.163  
   1.164 -performance not so important:
   1.165 -\name{postfix} focuses much on performance, this might not be an important point then.
   1.166  
   1.167 -security:
   1.168 -It seems as if all widely used \mta{}s provide good security nowadays. \name{qmail}'s architecture, also used in \name{postfix}, is generally seen to be conceptually more secure, however.
   1.169  
   1.170  
   1.171  
   1.172 -\paragraph{local mail delivery}
   1.173 -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.)
   1.174  
   1.175  
   1.176 -\paragraph{various protocols}
   1.177 -protocols like \NAME{SMTP} and \NAME{UUCP}, between which mail is transferred.\footnote{\sendmail{}'s initial purpose was moving mail between \NAME{UUCP}, \NAME{SMTP}, and \name{Berknet}.}
   1.178 +%todo: my own poll (?)
   1.179  
   1.180  
   1.181 +%<< complexity >> << security >> << simplicity of configuration and administration >> << flexibility of configuration and administration >> << code size >> << code quality >> << documentation (amount and quality) >> << community (amount and quality) >> << used it myself >> << had problems with it >>
   1.182  
   1.183  
   1.184 -
   1.185 -
   1.186 -
   1.187 -
   1.188 -<< complexity >> << security >> << simplicity of configuration and administration >> << flexibility of configuration and administration >> << code size >> << code quality >> << documentation (amount and quality) >> << community (amount and quality) >> << used it myself >> << had problems with it >>
   1.189 -
   1.190 -
   1.191 -<< quality criteria >> << standards of any kind >> << how to compare? >> << (bewertungsmatrix) objectivity >> << how many criteria for ``good''? >>
   1.192 +%<< quality criteria >> << standards of any kind >> << how to compare? >> << (bewertungsmatrix) objectivity >> << how many criteria for ``good''? >>