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

2

3 This chapter introduces a group of \mta{}s.

4 These will be presented to the reader in a short overview and with the most important facts.

5 The next chapter will show a comparison of the candidates in several disciplines.

6

7

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

9 ``Mail transfer agent'' is a term covering a variety of programs.

10 One thing is common to them: they transport email from one \emph{thing} to another.

11 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}.}

12

13 Beside this common property, \MTA{}s can be very different.

14 Some of them have \NAME{POP3} and/or \NAME{IMAP} servers included.

15 Some can fetch mails through these protocols.

16 Others have have every feature you can think of.

17 And maybe there are some that do nothing else, but transporting email.

18

19

20 \section{The ones not regarded here}

21 The candidates for the competition in the next chapter are a subset of the \MTA{}s available.

22 Comparision between totally different programs (apart of one function) makes not much sense.

23 One would not use a program for a job it is not suited for.

24 Therefor \mta{}s that are rarely similar to \masqmail\ are not regarded.

25

26 The first group of programs to sort out are the so called \name{groupware} programs.

27 These provide a whole lot of functions, including mail transfer, file storage, calendars, resource management, instant messaging and more.

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

29

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

31 They transfer mail only to defined \name{smart hosts}\index{smart host}\footnote{\MTA{}s that receives email and route it to the actual destination}.

32 Most \MTA{}s can be configured to act as such a forwarder.

33 But this is normally an additional functionality.

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

35

36 Third, only \emph{sendmail-compatible} \MTA{}s will be regarded in the competition.

37 Hence all \MTA{}s not having a \emph{sendmail-compatible} interface or not offering it as a compatibility addon, will not be covered here.

38 The reason is the heavy reliance of \unix\ systems on the existance of a programs called \path{sendmail}.

39 This has historical reasons. See section \ref{sec:sendmail} for further information.

40

41 Further more, only programs with source code available are regarded. %FIXME: why

42

43

44 \section{The competitors}

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

46

47 For the comparision, five programs of this group are taken.

48 These are: \sendmail, \name{qmail}, \name{postfix}, \name{exim} and \masqmail.

49 The four alternatives to \masqmail\ are the most important representatives of the regarded group.

50 %TODO: what about having one program as ``outsider'' ...?

51

52 Other, but not covered, group members are: %FIXME: are these all MTAs of that group? why these and not others?

53 %TODO: what about `courier-mta'?

54

55 % http://www.yolinux.com/TUTORIALS/LinuxTutorialMailMTA.html

56 % http://homepages.tesco.net/~J.deBoynePollard/Reviews/UnixMTSes/

57

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

59

60 \subsection{\sendmail}

61 \sendmail\ is the most popular \mta.

62 Since it was one of the first \MTA{}s and was shipped by many vendors of \unix\ systems.

63

64 The program was written by Eric Allman as the successor of his program \name{delivermail}.

65 \sendmail\ was first released with \NAME{BSD} 4.1c in 1983.

66 Allman was not the only one working on the program.

67 Other people developed own versions of it and a variety of flavors came up, especially in the late eighties when Allman was inactive.

68

69 \sendmail\ is focused on transfering mails between different protocols and networks, this lead to a very flexible (though complex) configuration.

70

71 The latest version is 8.14.3 from May 2008.

72 Further development will go into the project \name{MeTA1} which succeeds \sendmail.

73

74 More information can be found on the \sendmail\ homepage \citeweb{sendmail:homepage} and on \citeweb{wikipedia:sendmail} and \citeweb{jdebp}.

75 %FIXME: license

76

77

78 \subsection{\name{qmail}}

79 \name{qmail} is seen by its community as ``a modern SMTP server which makes sendmail obsolete''.

80 It was written by Daniel~J.\ Bernstein starting in 1995.

81 His primary goal was to create a secure \MTA\ to replace the popular, but vulnerable, \sendmail.

82

83 \name{qmail} first introduced may innovative concepts in \mta\ design and is generally seen as the first security-aware \MTA\ developed.

84

85 Since November 2007, \name{qmail} is released in the \name{public domain} which makes it \freesw.

86 The latest release is 1.03 from July 1998.

87

88 The programs homepages are \citeweb{qmail:homepage1} and \citeweb{qmail:homepage2}. Further information about \name{qmail} is available on \citeweb{lifewithqmail}, \citeweb{wikipedia:qmail} and \citeweb{jdebp}.

89

90

91 \subsection{\name{postfix}}

92 %TODO: author, date of first release, basic intention of program, ...

93 %TODO: references to various descriptions

94

95 \subsection{\name{exim}}

96 %TODO: author, date of first release, basic intention of program, ...

97 %TODO: references to various descriptions

98

99 \subsection{\masqmail}

100 The \masqmail\ program was written by Oliver Kurth, starting in 1999.

101 His aim was to create a \mta\ which is especially focused on computers with dial-up connections to the internet.

102 \masqmail\ handles situations which are rarely solveable with the common \MTA{}s.

103 %TODO: references to various descriptions

104

105

106 % briefly discuss the border between small MTAs (sendmail, masqmail) and state-of-the-art mailservers (postfix) and groupware (notes, exchange): give usecases.