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1 \chapter{\unix\ \MTA{}s}
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2
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3 This chapter introduces a group of \mta{}s.
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4 These will be presented to the reader in a short overview and with the most important facts.
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5 The next chapter will show a comparison of the candidates in several disciplines.
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6
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7
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8 \section{Types of \MTA{}s}
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9 ``Mail transfer agent'' is a term covering a variety of programs.
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10 One thing is common to them: they transport email from one \emph{thing} to another.
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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}.}
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12
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13 Beside this common property, \MTA{}s can be very different.
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14 Some of them have \NAME{POP3} and/or \NAME{IMAP} servers included.
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15 Some can fetch mails through these protocols.
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16 Others have have every feature you can think of.
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17 And maybe there are some that do nothing else, but transporting email.
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18
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19
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20 \section{The ones not regarded here}
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21 The candidates for the competition in the next chapter are a subset of the \MTA{}s available.
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22 Comparision between totally different programs (apart of one function) makes not much sense.
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23 One would not use a program for a job it is not suited for.
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24 Therefor \mta{}s that are rarely similar to \masqmail\ are not regarded.
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25
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26 The first group of programs to sort out are the so called \name{groupware} programs.
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27 These provide a whole lot of functions, including mail transfer, file storage, calendars, resource management, instant messaging and more.
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28 Examples for this kind of programs are: \name{Lotus Notes}, \name{Microsoft Exchange}, \name{OpenGroupware.org} and \name{eGroupWare}.
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29
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30 The second group are the \name{relay-only} \MTA{}s.
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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}.
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32 Most \MTA{}s can be configured to act as such a forwarder.
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33 But this is normally an additional functionality.
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34 Examples for that group are: \name{nullmailer}, \name{ssmtp} and \name{esmtp}.
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35
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36 Third, only \emph{sendmail-compatible} \MTA{}s will be regarded in the competition.
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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.
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38 The reason is the heavy reliance of \unix\ systems on the existance of a programs called \path{sendmail}.
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39 This has historical reasons. See section \ref{sec:sendmail} for further information.
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40
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41 Further more, only programs with source code available are regarded. %FIXME: why
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42
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43
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44 \section{The competitors}
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45 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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46
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47 For the comparision, five programs of this group are taken.
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48 These are: \sendmail, \name{qmail}, \name{postfix}, \name{exim} and \masqmail.
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49 The four alternatives to \masqmail\ are the most important representatives of the regarded group.
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50 %TODO: what about having one program as ``outsider'' ...?
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51
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52 Other, but not covered, group members are: %FIXME: are these all MTAs of that group? why these and not others?
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53 %TODO: what about `courier-mta'?
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54
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55 % http://www.yolinux.com/TUTORIALS/LinuxTutorialMailMTA.html
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56 % http://homepages.tesco.net/~J.deBoynePollard/Reviews/UnixMTSes/
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57
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58 Here follows a small introduction to each of the five.
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59
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60 \subsection{\sendmail}
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61 %TODO: author, date of first release, basic intention of program, ...
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62 %TODO: references to various descriptions
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63 %\citeweb{homepage:sendmail},
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64 \citeweb{wikipedia:sendmail}, \citeweb{jdebp}
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65
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66 \subsection{\name{qmail}}
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67 %TODO: author, date of first release, basic intention of program, ...
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68 %TODO: references to various descriptions
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69
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70 \subsection{\name{postfix}}
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71 %TODO: author, date of first release, basic intention of program, ...
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72 %TODO: references to various descriptions
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73
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74 \subsection{\name{exim}}
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75 %TODO: author, date of first release, basic intention of program, ...
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76 %TODO: references to various descriptions
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77
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78 \subsection{\masqmail}
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79 The \masqmail\ program was written by Oliver Kurth, starting in 1999.
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80 His aim was to create a \mta\ which is especially focused on computers with dial-up connections to the internet.
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81 \masqmail\ handles situations which are rarely solveable with the common \MTA{}s.
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82 %TODO: references to various descriptions
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83
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84
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85 % briefly discuss the border between small MTAs (sendmail, masqmail) and state-of-the-art mailservers (postfix) and groupware (notes, exchange): give usecases.
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