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date Tue, 13 Jan 2009 17:18:40 +0100
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81 \section{The \masqmail\ project} 81 \section{The \masqmail\ project}
82 \label{sec:masqmail} 82 \label{sec:masqmail}
83 83
84 << about masqmail (some history) >> 84 The \masqmail\ project was by \person{Oliver Kurth} in 1999. His aim was to create a small \mta\ that is especially focused on computers with dial-up Internet connections. Thoughout the next four years, he worked steadily on it, releasing new versions very few weeks. In total it were 53 releases, which means a new version in less than every 20 days in average.
85 85
86 (include history of email, definition of MTA and sendmail-compatibility in text) 86 This thesis bases on the latest release of \masqmail\ that was found---version 0.2.21 from November 2005. It was a release without source code changes to 0.2.20; only build documents were changed. One may retrieve it from the \debian\ package pool\footnote{The distribution tarball of \masqmail\ version 0.2.21 is located at: \url{http://ftp.de.debian.org/debian/pool/main/m/masqmail/masqmail\_0.2.21.orig.tar.gz}\,.} \citeweb{debian:packages}. It probably was never put into public anywhere else, including its homepage \citeweb{masqmail:homepage2}.
87 87
88 The \masqmail\ program was written by \person{Oliver 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. 88 \masqmail\ is covered by the \name{General Public License} (short: \GPL), which qualifies it as \freesw.
89 89
90 \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. 90 \person{Kurth} abandonned \masqmail\ after 2005, and no one addopted the project since then. Thus, the author of this thesis decided to take responsibility for \masqmail\ now. He received \person{Kurth}'s permission to do so.
91 91
92 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. 92 The program's new homepage is a collection of available information about this \MTA\ \citeweb{masqmail:homepage}.
93 93
94 \masqmail\ is released under the \GPL, which makes it \freesw. The latest stable version is 0.2.21 from November 2005. 94
95 95
96 The program's new homepage \citeweb{masqmail:homepage} provides further information about this \MTA. 96
97 97 \subsection{Target field of \masqmail}
98 << specify the really important external documents here >> %FIXME 98
99 99 The intention \person{Kurth} had when creating \masqmail\ is best told in his own words:
100
101
102 \subsection{Target field / When to use \masqmail}
103
104 Its original author, \person{Oliver Kurth}, sees \masqmail\ so:
105 \begin{quote} 100 \begin{quote}
106 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. 101 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.
102 \hfill\citeweb{masqmail:homepage2}
107 \end{quote} 103 \end{quote}
108 104 It is inteded to cover a specific niche: non-permanent internet connection and different \NAME{ISP}s.
109 \masqmail\ is inteded to cover a specific niche: non-permanent internet connection and different \NAME{ISP}s. 105
110 106 Although it can basically replace other \MTA{}s, it is not \emph{generally} aimed to do so. The package description of \debian\ states this more clearly by changing the last sentence to:
111 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:
112 \begin{quote} 107 \begin{quote}
113 In these cases, MasqMail is a slim replacement for full-blown MTAs such as sendmail, exim, qmail or postfix. 108 In these cases, MasqMail is a slim replacement for full-blown MTAs such as sendmail, exim, qmail or postfix.
109 \hfill\citeweb{packages.debian:masqmail}
114 \end{quote} 110 \end{quote}
115 \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. 111 The program is a good replacement ``in these cases'', but not generally, since is lacks essential features for running on mail servers. It is primarily not secure enough for being accessable from untrusted locations.
116 112
117 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. 113 \masqmail\ is best used in home networks, which are non-permanently connected to the Internet. It is easy configurable for situations which are rarely solveable with the common \MTA{}s. Such include different handling of mail to local or remote destination and respecting different routes of being online connection. These features are explained in more detail in the following \name{Features} section on page \ref{sec:masqmail-features}. %fixme: is it still called ``features''?
118 114
119 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. 115 While many other \MTA{}s are general purpose \MTA{}s, \masqmail\ aims on special situations. Nevertheless, it can be used as general purpose \MTA, too. Especially this was a design goal of \masqmail: To be a replacement for \sendmail, or similar well known \MTA{}s.
120 116
121 117 \masqmail\ is designed to run on workstations and on servers in small networks, like home networks.
122 118
123 119
124 \subsubsection*{\masqmail's main goal} 120
125 121 \subsubsection*{A typical usage scenario}
126 \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: 122
123 This section describes two common setups that makes senseful use of \masqmail.
124
125 Imagine 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 network. \NAME{IP} addresses change at least once every day.
126
127 Every workstation would be equiped with \masqmail. Mail transfer within the same machine or within the local net works straight forward using direkt transfer. Outgoing mail to the internet is sent, to an \name{Internet Service Provider} (short: \NAME{ISP}) for relaying whenever the router goes online. To receive mail from the Internet requires a mailbox on the \NAME{ISP}'s mail server. Mail needs to be fetched from the \NAME{ISP}'s server onto the workstation. The configuration of \masqmail\ would be the same on every computer, except different hostnames.
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129 In the same network but with a server, one could have \masqmail\ running on the server and using simple forwarders (see \ref{subsec:relay-only}) on the workstations to tranfer mail to the server. The server would then deliver locally or relay to an \NAME{ISP}'s server for further relay, dependent on the destination of the message. This setup does only support mail transfer to the server, but not back to a workstation. This transfer from the server to the workstations can be solvable by mounting the users mailbox from the server to the workstation, or by making the workstations fetch mail from the server.
130
131 %fixme: what about notebooks?
132 << notebooks >>
133
134 Figure \ref{fig:masqmail-typical-usage} despicts the two scenarios.
135
136 \begin{figure}
137 \begin{center}
138 \includegraphics[scale=0.75]{img/masqmail-typical-usage.eps}
139 \end{center}
140 \caption{Typical usage scenarios for \masqmail}
141 \label{fig:masqmail-typical-usage}
142 \end{figure}
143
144 In general, all kinds of usage scenarios within a trusted network are possible.
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147
148
149 \subsubsection*{Limitations}
150
151 Although \masqmail\ is seen as a replacement for other general purpose \MTA{}s, it should not be used on large mail servers. The reasons are that it implements only a basic subset of features, also its performance and security are not as good as provided by alternative \MTA{}s.
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153 The author, \person{Kurth}, warns on the old project's website about using it to accept connections from the Internet, because of the risk of being an open relay:
154
127 \begin{quote} 155 \begin{quote}
128 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. 156 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.
157 \hfill\citeweb{masqmail:homepage2}
129 \end{quote} 158 \end{quote}
159
130 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. 160 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.
131 161
132 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. 162 Hence, \masqmail\ should not be used for permanent internet connections. Or at least it needs to be secured with care.
133 163
134 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. 164
135
136
137 \subsubsection*{Full featured or stripped down}
138
139 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?
140
141 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.
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143 \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.
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145 This is not what \masqmail\ was intended to be. Programs that cover this purpose are available; one is \name{msmtp}.
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147 \masqmail\ shall be a complete \mta. It shall be able to replace ones like \sendmail.
148
149
150
151 \subsubsection*{Typical usage}
152 This section describes situations that make senseful use of \masqmail.
153
154 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.
155
156 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.
157
158 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.
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160 A better setup is to run \masqmail\ on every machine %FIXME
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165
166
167 \subsection{When not to use \masqmail}
168
169 ...
170 165
171 166
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173 168
174 169
212 207
213 208
214 \subsubsection*{Online detection and routes} 209 \subsubsection*{Online detection and routes}
215 \label{sec:masqmail-routes} 210 \label{sec:masqmail-routes}
216 211
212 \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.
213
214 \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.
215
216 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.
217 --- 217 ---
218 218
219 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. 219 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.
220 220
221 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. 221 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.