docs/diploma

annotate thesis/tex/1-Introduction.tex @ 229:c5f44219bc5d

added text parts to intro
author meillo@marmaro.de
date Fri, 09 Jan 2009 14:22:06 +0100
parents aab8499c9f2f
children d60e5843db7f
rev   line source
meillo@26 1 \chapter{Introduction}
meillo@42 2 \label{chap:introduction}
meillo@26 3
meillo@96 4 << say what you want to say >>
meillo@92 5
meillo@102 6 << the overall goal of the document >>
meillo@92 7
meillo@92 8
meillo@92 9
meillo@229 10 \section{What's an MTA?}
meillo@229 11
meillo@229 12 The basic job of a \mta\ is to transport mail from senders to recipients. This is the definition of such kind of software, and this is how \MTA{}s are generally seen \cite[page 19]{dent04} \cite[pages 3-5]{hafiz05}.
meillo@229 13
meillo@229 14 An \MTA\ therefore needs at least a mail receiving facility and a mail sending facility.
meillo@229 15
meillo@229 16 << structure diagram of an MTA (and of masqmail) >>
meillo@229 17
meillo@229 18
meillo@229 19
meillo@229 20
meillo@229 21
meillo@92 22 \section{The \masqmail\ project}
meillo@102 23 \label{sec:masqmail}
meillo@96 24
meillo@96 25 << about masqmail (some history) >>
meillo@96 26
meillo@96 27 (include history of email, definition of MTA and sendmail-compatibility in text)
meillo@96 28
meillo@142 29 The \masqmail\ program was written by Oliver \person{Kurth}, starting in 1999. His aim was to create a small \mta\ which is especially focused on computers with dial-up connections to the internet. \masqmail\ is easy configurable for situations which are rarely solveable with the common \MTA{}s.
meillo@102 30
meillo@102 31 \masqmail\ queues mail for destinations outside the local network if no connection to the internet is online. If the machine goes online, this mail is sent. Mail to local machines is sent immediately.
meillo@102 32
meillo@102 33 While the other \MTA{}s are more general purpose \MTA{}s, \masqmail\ aims on special situations only. Nevertheless can it handle ordinary mail transfers too.
meillo@102 34
meillo@102 35 \masqmail\ is released under the \GPL, which makes it \freesw. The latest stable version is 0.2.21 from November 2005.
meillo@102 36
meillo@102 37 The program's new homepage \citeweb{masqmail:homepage} provides further information about this \MTA.
meillo@96 38
meillo@92 39
meillo@160 40 \subsubsection*{Target field}
meillo@160 41
meillo@142 42 Its original author, Oliver \person{Kurth}, sees \masqmail\ so:
meillo@92 43 \begin{quote}
meillo@92 44 MasqMail is a mail server designed for hosts that do not have a permanent internet connection eg. a home network or a single host at home. It has special support for connections to different ISPs. It replaces sendmail or other MTAs such as qmail or exim.
meillo@92 45 \end{quote}
meillo@92 46
meillo@92 47 \masqmail\ is inteded to cover a specific niche: non-permanent internet connection and different \NAME{ISP}s.
meillo@92 48
meillo@92 49 Although it can basically replace other \MTA{}s, it is not generally aimed to do so. The package description of \debian\citeweb{packages.debian:masqmail} states this more clearly by changing the last sentence to:
meillo@92 50 \begin{quote}
meillo@92 51 In these cases, MasqMail is a slim replacement for full-blown MTAs such as sendmail, exim, qmail or postfix.
meillo@92 52 \end{quote}
meillo@92 53 \masqmail\ is a good replacement ``in these cases'', but not generally, since is lacks features essential for running on mail servers. It is primarily not secure enough for being accessable from untrusted locations.
meillo@92 54
meillo@92 55 The program is best used in home networks, which are non-permanently connected to the internet. \masqmail\ sends mail to local destinations, like users on the same machine and on other machines in the local net, immediately. Email to recipients outside the local net are queued when offline and sent when a online connection gets established.
meillo@92 56
meillo@92 57 Further more does \masqmail\ respect online connections through different \NAME{ISP}s; a common thing for dial-up connections. In particular can different sender addresses be set, dependent on the \NAME{ISP} that is used. This prevents mail to be likely classified as spam.
meillo@92 58
meillo@92 59
meillo@92 60
meillo@160 61 \subsubsection*{Typical usage}
meillo@92 62 This section describes situations that make senseful use of \masqmail.
meillo@92 63
meillo@92 64 A home network consisting of some workstations without a server. The network is connected to the internet by dial-up or broadband. Going online is initiated by computers inside the local net. \NAME{IP} addresses change at least once every day.
meillo@92 65
meillo@92 66 Every workstation would be equiped with \masqmail. Mail transfer within the same machine or within the local net works straight forward. Outgoing mail to the internet is sent, to the concerning \NAME{ISP} for relaying, whenever the router goes online. Receiving of mail from outside needs to be done by a mail fetch program, like the \masqmail\ internal \NAME{POP3} client or \name{fetchmail} for example. The configuration for \masqmail\ would be the same on every computer, except the hostname.
meillo@92 67
meillo@92 68 For the same network but having a server, one could have \masqmail\ running on the server and using simple forwarders (see \ref{subsec:relay-only}) to the server on the workstations. This setup does only support mail transfer to the server, but not back to a workstation; also sending mail to another user on the same workstation is not possible.
meillo@92 69
meillo@92 70 A better setup is to run \masqmail\ on every machine %FIXME
meillo@92 71
meillo@92 72
meillo@229 73 \subsubsection{Online detection and routes}
meillo@229 74 \label{sec:masqmail-routes}
meillo@229 75
meillo@135 76 ---
meillo@135 77
meillo@135 78 As \masqmail\ is focused on non-permanent Internet connections, online state can be queried by three methods: reading from a file, reading the output of a command, or by asking an \name{mserver}. Each method may return a string indicating one of the available routes being online, or returning nothing to indicate offline state.
meillo@135 79
meillo@135 80 Delivery to recipients on the local host or in local nets is done at once; delivery to recipients on the Internet is only done when being online, and queued otherwise. Each online route may have a different mail server to which mail is relayed. Return address headers are modified appropriate if wished.
meillo@135 81
meillo@135 82 ---
meillo@135 83
meillo@229 84 \masqmail\ focuses on non-permanent online connections, thus a concept of online routes is used. One may configure any number of routes to send mail. Each route can have criteria, like matching \texttt{From:} or \texttt{To:} headers, to determine if some message is allowed to be sent over it. Mail to destinations outside the local network gets queued until an online connections is available.
meillo@229 85
meillo@92 86
meillo@160 87
meillo@160 88
meillo@160 89
meillo@160 90 \subsubsection*{\masqmail's main goal}
meillo@160 91
meillo@160 92 \masqmail\ does have similar requirements, by being a \sendmail\ replacement, which is a basic goal of the project. The main difference is that \masqmail\ is intended to be used on workstations and in small networks, but \sendmail, \qmail, and \postfix\ are designed to run on large mail servers to handle masses of email. The author of \masqmail, \person{Kurth}, in contrast, warns on the old project's website \citeweb{masqmail:homepage2} about using it to accept connections from the Internet, because of the risk to be an open relay:
meillo@160 93 \begin{quote}
meillo@160 94 MasqMail is not designed to run on a host with a permanent internet connection. It does not have the ability to check for spam mail and it will relay everything from everywhere to everywhere. Use another mail server such as exim for permanent connections.
meillo@160 95 \end{quote}
meillo@160 96 Even if some relay control will be added, ``is not designed to'' is a clear indicator for being careful. Issues like high memory consumption, low performance, and denial-of-service attacks---things not regarded by design---may cause serious problems.
meillo@160 97
meillo@160 98 Here shows a misfit off: On the one hand does \masqmail\ want to be a \sendmail\ replacement. But on the other hand, is it not designed to be used like \sendmail. If \masqmail\ is inteded to replace other \MTA{}s, then one may replace another one with it. Hence it must be secure enough. It either needs the security features or must drop the unsecure funtionality. The second option, however, leads to being \emph{no} replacement for other \MTA{}s. It is a valid decision to not be a replacement for \sendmail\ or thelike, but this is a design decision---the change of a primary goal.
meillo@160 99
meillo@160 100 If \masqmail\ should be an \MTA\ to replace others, a switch to a better suited architecture that provides good security and extendability by design, seems required. But if \masqmail\ is wanted to cover some special jobs, not to replace common \MTA{}s, then its architecture depends on the special requirements of the specific job; \MTA\ architectures, like discussed by \person{Hafiz}, may be inadequate.
meillo@160 101
meillo@160 102
meillo@160 103 \subsubsection*{Full featured or stripped down}
meillo@160 104
meillo@160 105 What future is to choose for \masqmail---one to be a full featured \MTA, or one to be a stipped down \MTA\ for special jobs?
meillo@160 106
meillo@160 107 The critical point to discuss upon is surely the listening on a port to accepte messages from outside via \NAME{SMTP} (herafter also refered to as the \NAME{SMTP}-in channel). This feature is required for an \MTA\ to be a \name{smart host}, to relay mail. But running as deamon and listening on a port requires much more security effort, because the program is put in direct contact with attackers and other bad guys.
meillo@160 108
meillo@160 109 \MTA{}s without \SMTP-in channels can not receive mail from arbitrary outside hosts. They are only invoked by local users. This lowers the security need a lot---however, security is a general goal and still required, but on a lower level. Unfortunately, as they do not receive mail anymore (except by local submission), they are just better \name{forwarders} that are able to send mail directly to the destination.
meillo@160 110
meillo@160 111 This is not what \masqmail\ was intended to be. Programs that cover this purpose are available; one is \name{msmtp}.
meillo@160 112
meillo@160 113 \masqmail\ shall be a complete \mta. It shall be able to replace ones like \sendmail.
meillo@160 114
meillo@160 115
meillo@160 116
meillo@160 117
meillo@160 118
meillo@160 119
meillo@160 120
meillo@160 121
meillo@160 122 \subsubsection*{What makes it special}
meillo@92 123
meillo@92 124 As main advantage, \masqmail\ makes it easy to set up an \MTA\ on workstations or notebooks without the need to do complex configuration or to be an mail server expert.
meillo@92 125
meillo@92 126 Workstations use %FIXME
meillo@92 127
meillo@96 128 \textbf{Alternatives?}
meillo@92 129 % http://anfi.homeunix.org/sendmail/dialup10.html
meillo@92 130
meillo@92 131
meillo@92 132
meillo@96 133 << explain why masqmail is old and why it is interesting/important however! >> %FIXME
meillo@96 134
meillo@175 135 << why is it worth to revive masqmail? >>
meillo@175 136
meillo@96 137
meillo@96 138
meillo@92 139 \section{Problems to solve}
meillo@92 140
meillo@96 141 << what problems has masqmail? >> %FIXME
meillo@96 142
meillo@96 143 << what's the intention of this document? >> %FIXME
meillo@96 144
meillo@96 145 << why is it worth the effort? >> %FIXME
meillo@96 146
meillo@96 147
meillo@150 148 \section{What is not covered here}
meillo@96 149
meillo@150 150 << limit against stuff not covered here >>
meillo@96 151
meillo@96 152
meillo@96 153 \section{Further reading}
meillo@96 154
meillo@150 155
meillo@96 156 << specify the really important external documents here >> %FIXME
meillo@96 157
meillo@96 158 << write about the bundled CD, and tell what's included >> %FIXME
meillo@96 159
meillo@96 160 \NAME{RFC}s, other books, source code, websites
meillo@96 161
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meillo@133 163