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1 \chapter{Introduction}
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2 \label{chap:introduction}
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3
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4 \section{History of electronic mail}
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5 %TODO: have a quote from Bell Labs about email here
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6 %FIXME: add references to text
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7
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8 Electronic mail\index{electronic mail@electronic mail (email)} (short: \name{email}) is a basic concept in \unix.
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9 On \unix\ machines, a lot of information is distributed by \name{system mail}, which is email sent by the operating system.
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10 Beside that, email is the common communication system between humans working on computers.
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11
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12 The \unix\ operating system supports email since 1979 through the \name{mail user agent} (\NAME{MUA}) \path{/bin/mail}.
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13 For transporting mail in between two systems, the \NAME{UUCP} protocol (for ``\unix\ to \unix\ copy'') was invented.
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14 %FIXME: what about `uuxqt' and `rmail'
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15
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16 As generally known, the early development of \unix\ was not only made in the \name{Bell Labratories} of \NAME{AT\&T}.
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17 But also the \name{Univerity of California at Berkeley} worked on their version of a \unix\ operating system, called \NAME{UCB} \unix, or \name{Berkeley} \unix.
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18
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19 This lead to a second \NAME{MUA} from Berkeley: \name{Mail} (with a capital `M').
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20 Also, no \NAME{UUCP} network was set up at Berkeley but an own creation called \name{Berknet} was used.
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21 %FIXME: why? license issues? closed source?
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22 %TODO: what about `mailx'?
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23
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24 Further more there was a third network type: the \NAME{ARPAnet}, based on the \name{transmission control protocol} (\NAME{TCP}).
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25 %FIXME: where did it came from?
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26
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27 Each of the three network types could transfer email between different machines.
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28 The file transfer itself was made using \NAME{FTP}, but the higher layered logic of the transfer was different in each.
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29 For example was the addressing schema not the same: \NAME{UUCP} used a flat-style schema, while \NAME{ARPAnet} was hierachical.
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30
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31 Mail transport from one machine using one kind of network to a second machine using another kind was a problem.
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32 This showed up at Berkeley where some departments of the university had switched to \NAME{ARPAnet}, and some to \NAME{UUCP}, while the rest was \name{Berknet}.
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33
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34 It was around 1982, when Eric Allman, then a student at Berkeley, wrote \name{delivermail}.
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35 Its purpose was to transform email from one network to another.
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36 \name{delivermail} like its successor, the more flexible \sendmail, intermediated between the different networks.
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37 They were able to transform email messages from any network to any other.
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38
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39 Todays email structure is basicly the same as then.
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40 The major difference is the uniformity of the underlying network, which is nearly always the \NAME{ARPAnet}-based \name{Internet}.
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41 Most other differences are organized as extensions to the old model of electronic mail.
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42
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43 More information about electronic mail and its history can be found at:
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44 %FIXME: add books and websites here
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45
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46
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47
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48 \section{Transporting mail}
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49 %TODO: include definitions from others here (cites)
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50 %TODO: when was the term ``mail transfer agent'' established?
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51 The basic job of a \name{mail transfer agent} (or \index{mail transport agent|see{mail transfer agent}}\name{mail transport agent}, short \NAME{MTA}) is to transfer/transport \name{electronic mail} (short \name{email}) from one host to another.
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52
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53
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54
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55
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56 \section{\sendmail}
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57 \label{sec:sendmail}
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58 \name{sendmail} is the de facto standard for \name{mail transfer agents}.
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59
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60 % FIXME: is that true?
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61 It was the first \NAME{MTA} and had no real alternative for a long time.
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62
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63 All other existing substitutes, which are mainly \name{postfix}, \name{exim}, \name{qmail} and the here regarded \name{masqmail}, mimic \name{sendmail}'s behavior.
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64 Especially, they all create a symbolic link named ``sendmail'' pointing to their own executable.
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65 This is because a lot of programs assume there is an executable called ``sendmail'' on every computer system.
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66
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67 Besides being the ``standard'', \name{sendmail} probably is the most scalable and powerful solution for transfering emails and definatly the most flexible one.
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68
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69
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70
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71 \section{(a look at Windows)}
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72
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