1 \chapter{\unix\ \MTA{}s}

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3 This chapter introduces a group of \mta{}s. These will be presented to the reader in a short overview and with the most important facts. The next chapter will show a comparison of the candidates in several disciplines.

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6 \section{Types of \MTA{}s}

7 ``Mail transfer agent'' is a term covering a variety of programs. One thing is common to them: they transport email from one \emph{thing} to another. These \emph{things} can be hosts, meaning independent machines, or protocols like \NAME{SMTP} and \NAME{UUCP}, between which mail is transfered.\footnote{\sendmail{}'s initial purpose was moving mail between \NAME{UUCP}, \name{Berknet} and \NAME{SMTP}.}

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9 Beside this common property, \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 have every feature you can think of. And maybe there are some that do nothing else, but transporting email.

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12 \section{The ones not regarded here}

13 The candidates for the competition in the next chapter are a subset of the \MTA{}s available. Comparision between totally different programs (apart of one function) makes not much sense. One would not use a program for a job it is not suited for. Therefor \mta{}s that are rarely similar to \masqmail\ are not regarded.

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15 The first group of programs to sort out are the so called \name{groupware} programs. These provide a whole lot of functions, including mail transfer, file storage, calendars, resource management, instant messaging and more.

16 Examples for this kind of programs are: \name{Lotus Notes}, \name{Microsoft Exchange}, \name{OpenGroupware.org} and \name{eGroupWare}.

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18 The second group are the \name{relay-only} \MTA{}s.

19 They transfer mail only to defined \name{smart hosts}\index{smart host}\footnote{MTAs that receives email and route it to the actual destination}. Most \MTA{}s can be configured to act as such a forwarder. But this is normally an additional functionality.

20 Examples for that group are: \name{nullmailer}, \name{ssmtp} and \name{esmtp}.

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22 Third, only \emph{sendmail-compatible} \MTA{}s will be regarded in the competition. The ones not \emph{sendmail-compatible} are not from big interest on \unix\ systems. %FIXME: write it the other way round: the group sorted out.

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25 \section{The competitors}

26 %FIXME: are these all MTAs of that group? why these and not others?

27 %TODO: what about `courir-mta'?

28 The programs remaining are \emph{sendmail-compatible} ``smart'' \MTA{}s that do not offer masses of features unrelated to mail transport.

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30 For the comparision, five programs of this group are taken. These are: \sendmail, \name{qmail}, \name{postfix}, \name{exim} and \masqmail. The four alternatives to \masqmail\ are the most important representatives of the regarded group.

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32 Here follows a small introduction to each of the five.

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34 \subsection{\sendmail}

35 %TODO: author, date of first release, basic intention of program, ...

36 %TODO: references to various descriptions

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38 \subsection{\name{qmail}}

39 %TODO: author, date of first release, basic intention of program, ...

40 %TODO: references to various descriptions

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42 \subsection{\name{postfix}}

43 %TODO: author, date of first release, basic intention of program, ...

44 %TODO: references to various descriptions

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46 \subsection{\name{exim}}

47 %TODO: author, date of first release, basic intention of program, ...

48 %TODO: references to various descriptions

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50 \subsection{\masqmail}

51 The \masqmail\ program was written by Oliver Kurth, starting in 1999. His aim was to create a \mta\ which is especially focused on computers with dial-up connections to the internet. \masqmail\ handles situations which are rarely solveable with the common \MTA{}s.

52 %TODO: references to various descriptions

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