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author meillo@marmaro.de
date Sun, 08 Feb 2009 23:15:35 +0100
parents 5254a119ad56
children 1d527ad76c97
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meillo@26 1 \chapter{Introduction}
meillo@42 2 \label{chap:introduction}
meillo@26 3
meillo@370 4 This chapter introduces some basic email concepts that are essential for understanding the remainder of the thesis. Then \masqmail---the program of interest---is presented. History, typical usage, and the function it provides are described. After an explanation of \masqmail's relevance, its weaknesses are pointed out. Solving these weaknesses is the topics that is covered throughout this thesis.
meillo@92 5
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meillo@245 9
meillo@245 10 \section{Email prerequisites}
meillo@245 11
meillo@402 12 Electronic mail is a service on the Internet and thus, like other Internet services, defined and standardized by \name{Requests For Comments} (short: \RFC{}s) under management of the \name{Internet Engineering Task Force} (short: \NAME{IETF}). \RFC{}s are highly technical documents and it is not required that the readers of this thesis are familiar with them.
meillo@402 13 \index{ietf}
meillo@402 14 \index{rfc}
meillo@306 15
meillo@370 16 This section gives an introduction into the basic internals of the email system in a low-technical language. It is intended to make the reader familiar with the essential concepts of email as they are essential throughout the thesis.
meillo@245 17
meillo@245 18
meillo@245 19 \subsubsection{Mail agents}
meillo@373 20 \index{mail agents}
meillo@245 21
meillo@378 22 This thesis will frequently use the three terms: \MTA, \MUA{}, and \MDA{}, naming the three different kinds of nodes of the email infrastructure. Here, they are explained with references to the ``snail mail'' system which is known from everyday life. Figure~\ref{fig:mail-agents} shows the relation between those three mail agents and the way an email message takes when passing through the system.
meillo@253 23
meillo@269 24 \begin{description}
meillo@269 25 \item[\MTA:]
meillo@373 26 \index{mta}
meillo@378 27 \name{Mail Transfer Agents} are the post offices for electronic mail. The basic job of an \MTA\ is to transport mail from senders to recipients, or more pedantic: from \MTA\ to \MTA. \sendmail, \exim, \qmail, \postfix, and, of course, \masqmail\ are \MTA{}s. \MTA{}s are explained in more detail in chapter~\ref{chap:mail-transfer-agents}.
meillo@245 28
meillo@373 29 \item[\MUA{}:]
meillo@373 30 \index{mua}
meillo@393 31 \name{Mail User Agents} are the software users deal with. A user writes and reads email with it. The \MUA{} passes outgoing mail to the nearest \MTA. Also the \MUA{} displays the contents of the user's mailbox. Well known \MUA{}s are \name{Mozilla Thunderbird} and \name{mutt} on Unix systems, and \name{Microsoft Outlook} on \name{Windows}.
meillo@245 32
meillo@373 33 \item[\MDA{}:]
meillo@373 34 \index{mda}
meillo@373 35 \name{Mail Delivery Agents} correspond to postmen in the real world. They receive mail, destined to recipients they are responsible for, from an \MTA, and deliver it to the mailboxes of those recipients. Many \MTA{}s include an own \MDA{}, but independent ones exist: \name{procmail} and \name{maildrop} are examples.
meillo@269 36 \end{description}
meillo@402 37 \index{procmail}
meillo@245 38
meillo@253 39 \begin{figure}
meillo@253 40 \begin{center}
meillo@397 41 \includegraphics[scale=0.75]{fig/mail-agents.eps}
meillo@253 42 \end{center}
meillo@253 43 \caption{Mail agents and the way a mail message takes}
meillo@253 44 \label{fig:mail-agents}
meillo@253 45 \end{figure}
meillo@245 46
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meillo@229 49
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meillo@229 51
meillo@245 52 \subsubsection{Mail transfer with SMTP}
meillo@396 53 \label{smtp-intro}
meillo@245 54
meillo@402 55 Today most of the email is transferred using the \name{Simple Mail Transfer Protocol} (short: \SMTP), which is defined in \RFC\,821 and the successors \RFC\,2821 and \RFC\,5321. A good entry point for further information is \citeweb{wikipedia:smtp}.
meillo@402 56 \index{smtp}
meillo@402 57 \index{rfc}
meillo@245 58
meillo@402 59 A selection of important concepts of \SMTP\ is explained here.
meillo@402 60 \index{smtp!concepts of}
meillo@245 61
meillo@402 62 First the \name{store-and-forward} transfer concept. This means mail messages are sent from \MTA\ to \MTA, until the final \MTA\ (the one which is responsible for the recipient) is reached. The message is stored for some time on each \MTA, until it is forwarded to the next \MTA.
meillo@402 63 \index{smtp!store-and-forward}
meillo@245 64
meillo@402 65 This leads to the concept of \name{responsibility}. A mail message is always in the responsibility of one system. First it is the \MUA. When it is transferred to an \MTA, this \MTA\ takes over the responsibility for the message, too. The \MUA{} can then delete its copy of the message. This is the same for each transfer---from \MTA\ to \MTA\ and finally from \MTA\ to the \MDA{}---the message gets transferred and if the transfer was successful, the responsibility for the message is transferred as well. The responsibility chain ends at a user's mailbox where he himself has control on the message.
meillo@402 66 \index{mua}
meillo@402 67 \index{mda}
meillo@402 68 \index{smtp!responsibility}
meillo@245 69
meillo@402 70 A third concept is about failure handling. At any step on the way an \MTA\ may receive a message it is unable to handle. In such a case this receiving \MTA\ will \name{reject} the message before it takes responsibility for it. The sending \MTA\ still has responsibility for the message and may try other ways for sending the message. If none succeeds the \MTA\ will send a \name{bounce message} back to the original sender with information on the type of failure. Bounces are only sent if the failure is expected to be permanent or if the transfer still was unsuccessful after many tries.
meillo@402 71 \index{smtp!bouncing}
meillo@402 72 \index{smtp!rejecting}
meillo@245 73
meillo@245 74
meillo@245 75
meillo@245 76 \subsubsection{Mail messages}
meillo@245 77
meillo@402 78 Mail messages consist of text in a specific format. This format is specified in \RFC\,822, and the successors \RFC\,2822 and \RFC\,5322.
meillo@402 79 \index{mail message}
meillo@402 80 \index{rfc}
meillo@245 81
meillo@402 82 A message has two parts, the \name{header} and the \name{body}. The header of an email message is similar to the header of a (formal) letter. It spans the first lines of the message up to the first empty line. The header consists of several lines, called \name{header lines} or simply \name{headers}. They specify the sender, the recipient(s), the date, and possibly further information. Their order is irrelevant. Headers are named like the colon-separated start of those lines, for example the ``\texttt{Date:}'' header. A user may write the header himself but normally the \MUA{} does this job.
meillo@245 83
meillo@402 84 The body is the payload of the message. It is under full control of the user. From the view point of the \SMTP\ protocol, it must consist of only 7-bit \NAME{ASCII} text. But arbitrary content can be included by encoding it to 7-bit \NAME{ASCII}. \NAME{MIME} is the common \SMTP\ extension to handle such conversion automatically in \MUA{}s.
meillo@402 85 \index{mua}
meillo@402 86 \index{mime}
meillo@402 87 \index{ascii}
meillo@245 88
meillo@253 89 Following is a sample mail message with four header lines (\texttt{From:}, \texttt{To:}, \texttt{Date:}, and \texttt{Subject:}) and three lines of message body.
meillo@245 90
meillo@402 91 \codeinput{input/sample-email.txt}
meillo@245 92
meillo@402 93 Email messages are put into \name{envelopes} for transfer. This concept is also derived from the real world so it is easy to understand. The envelope is used to route the message from sender to recipient. It contains the sender's address and addresses of one or more recipients. Envelopes are generated by \MTA{}s, usually from mail header data. The user has not to deal with them.
meillo@253 94
meillo@260 95 Each \MTA\ on the way reads envelopes it receives and generates new ones. If a message has recipients on different hosts, then the message gets copied and sent within multiple envelopes, one for each host.
meillo@260 96
meillo@402 97 The sample message would lead to two envelopes, one from \name{markus@host01} to \name{alice@host02}, the other from \name{markus@host01} to \name{bob@host03}. Both envelopes would contain the same message.
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meillo@229 102
meillo@229 103
meillo@92 104 \section{The \masqmail\ project}
meillo@102 105 \label{sec:masqmail}
meillo@96 106
meillo@402 107 The \masqmail\ project was initiated 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. Throughout the next four years he worked steadily on it, releasing new versions every few weeks. During the active phase of development 53 version have been released. In average, this is a new version every 20 days.
meillo@402 108 \index{masqmail}
meillo@402 109 \index{dial-up}
meillo@96 110
meillo@402 111 This thesis is based on the latest release of \masqmail---version 0.2.21, dated November 2005. It was released after a 28 month gap of inactivity. The source code of 0.2.21 is the same as of 0.2.20, with only build documents modified. The homepage of \masqmail\ \citeweb{masqmail:homepage2} does not include this latest release, but it can be retrieved from the \name{Debian} package pool\footnote{The \NAME{URL} is:\\\url{http://ftp.de.debian.org/debian/pool/main/m/masqmail/masqmail_0.2.21.orig.tar.gz}} \citeweb{packages.debian}.
meillo@402 112 \index{debian!package pool}
meillo@96 113
meillo@402 114 \masqmail\ is covered by the \name{General Public License} (short: \NAME{GPL}) version two or any later version \cite{fsf:gpl}. This qualifies \masqmail\ as Free Software \cite{fsf:freesw-definition}.
meillo@402 115 \index{gpl}
meillo@402 116 \index{Free Software}
meillo@102 117
meillo@370 118 \person{Kurth} abandoned \masqmail\ after 2005 and no one adopted the project since then. Thus, the author of this thesis decided to take over responsibility for \masqmail\ now. He received \person{Kurth}'s permission to do so in private telephone conversation with \person{Kurth} on September 4, 2008.
meillo@102 119
meillo@402 120 The program's new homepage \citeweb{masqmail:homepage} includes a collection of available information about this \MTA.
meillo@102 121
meillo@102 122
meillo@96 123
meillo@92 124
meillo@366 125 \subsection{Target field}
meillo@266 126 \label{sec:masqmail-target-field}
meillo@245 127
meillo@402 128 \person{Kurth}'s intention when creating \masqmail\ is best told in his own words:
meillo@402 129 \index{masqmail}
meillo@375 130
meillo@92 131 \begin{quote}
meillo@366 132 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 \NAME{ISP}s. It replaces sendmail or other \MTA{}s such as qmail or exim.
meillo@257 133 \hfill\citeweb{masqmail:homepage2}
meillo@257 134 \end{quote}
meillo@375 135
meillo@366 136 It is intended to cover a specific niche: non-permanent Internet connection and different \name{Internet Service Providers} (short: \NAME{ISP}s).
meillo@257 137
meillo@402 138 Although it can basically replace other \MTA{}s it is not \emph{generally} aimed to do so. The package description of \masqmail\ within \name{Debian} states this more clearly by changing the last sentence to:
meillo@402 139 \index{debian!masqmail package}
meillo@375 140
meillo@257 141 \begin{quote}
meillo@366 142 In these cases, MasqMail is a slim replacement for full-blown \MTA{}s such as sendmail, exim, qmail or postfix.
meillo@257 143 \hfill\citeweb{packages.debian:masqmail}
meillo@257 144 \end{quote}
meillo@257 145
meillo@375 146 The program is a good replacement ``in these cases'' but not generally, since it lacks essential features for running on publically accessable mail servers. It is primarily not secure enough for being accessible from untrusted locations.
meillo@257 147
meillo@402 148 \masqmail\ is best used in home networks which are non-permanently connected to the Internet. It is easy configurable for situations which are rarely solvable with the common \MTA{}s. Such include different handling of mail to local or remote destination and respecting different routes of online connection. These features are explained in more detail in section~\ref{sec:masqmail-features}.
meillo@402 149 \index{non-permanent online connection}
meillo@375 150
meillo@402 151 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 \MTA{}s.
meillo@402 152 \index{masqmail}
meillo@402 153 \index{sendmail}
meillo@257 154
meillo@370 155 \masqmail\ is designed to run on workstations and on servers in small networks, like they are common in \NAME{SOHO}s (\name{Small Offices/Home Offices}).
meillo@257 156
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meillo@257 158
meillo@260 159 \subsubsection*{Typical usage scenarios}
meillo@257 160
meillo@402 161 This section describes three common setups that make sensible use of \masqmail. The first two are shown in figure~\ref{fig:masqmail-typical-usage}.
meillo@402 162 \index{masqmail!common setups}
meillo@257 163
meillo@257 164 \begin{figure}
meillo@257 165 \begin{center}
meillo@397 166 \includegraphics[scale=0.75]{fig/masqmail-typical-usage.eps}
meillo@257 167 \end{center}
meillo@257 168 \caption{Typical usage scenarios for \masqmail}
meillo@257 169 \label{fig:masqmail-typical-usage}
meillo@257 170 \end{figure}
meillo@257 171
meillo@375 172 Imagine an Internet-connected home network consisting of some workstations.
meillo@260 173
meillo@269 174 \begin{description}
meillo@269 175 \item[Scenario 1:]
meillo@369 176 \label{scenario1}
meillo@402 177 If no server is present, every workstation would be equipped with \masqmail. Mail transfer within the same machine or within the local net works straight forward using direct transfer. Outgoing mail to the Internet is sent to an \name{Internet Service Provider} (short: \NAME{ISP}) for relaying whenever the router goes online. The configuration of \masqmail\ would be the same on every computer; only host names would differ. 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 using the \NAME{POP3} or \NAME{IMAP} protocol.
meillo@391 178 \index{isp}
meillo@391 179 \index{pop3}
meillo@391 180 \index{imap}
meillo@269 181
meillo@269 182 \item[Scenario 2:]
meillo@369 183 \label{scenario2}
meillo@378 184 In the same network but with a server, one could have \masqmail\ running on the server and using simple forwarders (see section~\ref{subsec:relay-only}) on the workstations to transfer mail to the server. The server would then, dependent on the destination of the message, deliver locally or relay to an \NAME{ISP}'s server for further relay. This setup does only support mail transfer to the server but not back to a workstation. However, this can be solved by mounting the user's mailbox from the server to the workstation or by using \NAME{POP3} or \NAME{IMAP}. Mail transfer from the \NAME{ISP} to the local server needs \NAME{POP3} or \NAME{IMAP} as well.
meillo@402 185 \index{relay-only mta}
meillo@391 186 \index{isp}
meillo@391 187 \index{pop3}
meillo@391 188 \index{imap}
meillo@269 189
meillo@269 190 \item[Scenario 3:]
meillo@369 191 \label{scenario3}
meillo@369 192 A third scenario is unrelated as it is about notebooks. Notebooks are usually used as mobile workstations. One uses them to work at different locations. With the increasing popularity of wireless networks this becomes more and more common. Different networks demand for different setups: In one network it is best to send mail to an \NAME{ISP} for relay. In another network it might be preferred to use a local mail server. A third network may have no Internet access at all, hence using a local mail server is required. All these different setups can be configured once and then used by simply telling the online state to \masqmail, even automatically within a network setup script.
meillo@391 193 \index{isp}
meillo@402 194 \index{masqmail!on notebooks}
meillo@269 195 \end{description}
meillo@269 196
meillo@269 197
meillo@374 198 In general, all kinds of usage scenarios within a trusted network are possible. Important to notice is that mail can not be sent from outside into the trusted network then. For using \masqmail\ on notebooks it is suggested to only accept mail from local users because notebooks are often in untrusted environments.
meillo@402 199 \index{untrusted environment}
meillo@257 200
meillo@257 201
meillo@257 202
meillo@257 203
meillo@257 204 \subsubsection*{Limitations}
meillo@391 205 \index{masqmail!limitations}
meillo@257 206
meillo@369 207 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 and that its performance and security is not as good as needed for such usage.
meillo@257 208
meillo@369 209 The author, \person{Kurth}, warns on the old project's website about using \masqmail\ to accept connections from the Internet because of the risk of being an open relay:
meillo@391 210 \index{open relay}
meillo@257 211
meillo@257 212 \begin{quote}
meillo@257 213 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@257 214 \hfill\citeweb{masqmail:homepage2}
meillo@92 215 \end{quote}
meillo@92 216
meillo@369 217 The actual problem is not the permanent Internet connection but listening for incoming mail on it. If a firewall is closed for incoming mail, then the permanent Internet connection is no problem. To use \masqmail\ for permanent Internet connections it needs to be secured with care.
meillo@391 218 \index{firewall}
meillo@160 219
meillo@392 220 The Internet is the common example for an untrusted network but other networks may be untrusted, too.
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meillo@245 231
meillo@245 232
meillo@245 233 \subsection{Features}
meillo@238 234
meillo@374 235 This thesis regards version 0.2.21 of \masqmail. This is the last version released by \person{Oliver Kurth}.
meillo@238 236
meillo@238 237
meillo@238 238 \subsubsection*{The source code}
meillo@238 239
meillo@369 240 \masqmail\ is written in the C programming language. The program, as of version 0.2.21, consists of 34 source code and eight header files which contain about 9\,000 lines of code\footnote{Measured with \name{sloccount} by David A.\ Wheeler \citeweb{sloccount}.}. Additionally, it includes a \name{base64} implementation (about 300 lines) and \name{md5} code (about 150 lines). For systems that do not provide \name{libident}, this library is distributed as well (circa 600 lines); an available shared library has higher precedence in linking, though.
meillo@391 241 \index{c}
meillo@391 242 \index{lines of code}
meillo@391 243 \index{base64}
meillo@391 244 \index{md5}
meillo@391 245 \index{libident}
meillo@238 246
meillo@238 247 The only mandatory dependency is \name{glib}---a cross-platform software utility library, originated in the \NAME{GTK+} project. It provides safe replacements for many standard library functions, especially for the string functions. It also offers handy data containers, easy-to-use implementations of data structures, and much more.
meillo@391 248 \index{glib}
meillo@391 249 \index{masqmail!dependencies}
meillo@238 250
meillo@369 251 Some parts of \masqmail's functionality can be included or excluded at compile time by defining symbols. To enable maildir support for example, one has to add \verb_--enable-maildir_ to the configure call. Otherwise the concerning code gets removed during preprocessing.
meillo@402 252 \index{conditional compilation}
meillo@391 253 \index{maildir}
meillo@260 254
meillo@369 255 With \masqmail\ comes the small tool \path{mservdetect}; it helps setting up a configuration that uses the \name{mserver} system for online state detection. Two other binaries get compiled for testing purposes: \path{readtest} and \path{smtpsend}. These three additional programs use parts of \masqmail's source code; they only add a file with a \verb+main()+ function each.
meillo@391 256 \index{mserver}
meillo@391 257 \index{test program}
meillo@238 258
meillo@238 259
meillo@238 260
meillo@238 261 \subsubsection*{Features}
meillo@238 262 \label{sec:masqmail-features}
meillo@238 263
meillo@369 264 \masqmail\ supports two channels for incoming mail:
meillo@369 265
meillo@369 266 \begin{enumerate}
meillo@391 267 \item Standard input which is used when \path{masqmail} (or the \path{sendmail} link) is executed on the command line
meillo@391 268 \item A \NAME{TCP} socket which is used by local or remote clients that talk \SMTP
meillo@369 269 \end{enumerate}
meillo@391 270 \index{sendmail!command}
meillo@391 271 \index{tcp socket}
meillo@369 272
meillo@369 273 The outgoing channels for mail are:
meillo@369 274
meillo@369 275 \begin{enumerate}
meillo@391 276 \item Direct delivery to local mailboxes (in \name{mbox} or \name{maildir} format)
meillo@402 277 \item Local pipes to pass mail to a program (e.g.\ to \MDA{}s or to gateways to \NAME{FAX} or \NAME{UUCP})
meillo@391 278 \item \NAME{TCP} sockets to transfer mail to other \MTA{}s using the \SMTP\ protocol
meillo@369 279 \end{enumerate}
meillo@391 280 \index{tcp socket}
meillo@391 281 \index{local delivery}
meillo@391 282 \index{mbox}
meillo@391 283 \index{maildir}
meillo@391 284 \index{uucp}
meillo@391 285 \index{fax}
meillo@391 286 \index{gateway}
meillo@402 287 \index{mda}
meillo@402 288 \index{pipe}
meillo@369 289
meillo@378 290 Figure~\ref{fig:masqmail-channels} shows this as a picture. (The ``online state'' input is explained a bit later.)
meillo@260 291
meillo@260 292 \begin{figure}
meillo@260 293 \begin{center}
meillo@397 294 \includegraphics[scale=0.75]{fig/masqmail-channels.eps}
meillo@260 295 \end{center}
meillo@260 296 \caption{Incoming and outgoing channels of \masqmail}
meillo@260 297 \label{fig:masqmail-channels}
meillo@260 298 \end{figure}
meillo@238 299
meillo@369 300 Outgoing \SMTP\ connections feature \SMTP-\NAME{AUTH} and \SMTP-after-\NAME{POP} authentication but incoming connections do not. Using wrappers for outgoing connections is supported. This allows encrypted communication through a gateway application like \name{openssl}.
meillo@402 301 \index{openssl}
meillo@402 302 \index{wrapper}
meillo@391 303 \index{auth!smtp-auth}
meillo@391 304 \index{auth!smtp-after-pop}
meillo@238 305
meillo@369 306 Mail queuing is essential for \masqmail\ and thus supported of course, alias expansion is also supported.
meillo@391 307 \index{alias expansion}
meillo@238 308
meillo@400 309 The \masqmail\ executable can be called by various names for sendmail-com\-pa\-ti\-bi\-li\-ty reasons. As many programs expect the \MTA\ to be located at \path{/usr/lib/sendmail} or \path{/usr/sbin/sendmail}, symbolic links are pointing from there to the \masqmail\ executable. Furthermore does \sendmail\ support calling it with a different name instead of supplying command line arguments. The best known of these shortcuts is \path{mailq} which is equivalent to calling it with the argument \verb+-bq+. \masqmail\ recognizes the shortcuts \path{mailq}, \path{smtpd}, \path{mailrm}, \path{runq}, \path{rmail}, and \path{in.smtpd}. The first two are inspired by \sendmail. Not implemented yet is the shortcut \path{newaliases} because \masqmail\ does not generate binary representations of the alias file.\footnote{A shell script named \path{newaliases} that invokes \texttt{masqmail -bi} can provide the command to satisfy strict requirements.} \path{hoststat} and \path{purgestat} are missing for complete sendmail-compatibility.
meillo@391 310 \index{sendmail!compatibility}
meillo@238 311
meillo@391 312 Additional to the \MTA\ job, \masqmail\ also offers mail retrieval services by acting as a \NAME{POP3} client. It can fetch mail from different remote locations, also dependent on the active online connection. Such functionality is especially useful in a setup like \name{Scenario 2} on page~\pageref{scenario2}.
meillo@391 313 \index{pop3}
meillo@238 314
meillo@238 315
meillo@238 316
meillo@370 317 \subsubsection*{Online detection and online routes}
meillo@245 318 \label{sec:masqmail-routes}
meillo@402 319 \index{online routes}
meillo@238 320
meillo@275 321 \masqmail\ focuses on handling different 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 to determine if some message is allowed to be sent over it. Mail to destinations outside the local network gets queued until a suitable online connections is available.
meillo@402 322 \index{non-permanent online connection}
meillo@260 323
meillo@370 324 The idea behind this concept is sending mail to the Internet through the mail server of the same \NAME{ISP} over which one had dialed in. It was quite common that \NAME{ISP}s accepted mail for relay only if it came from a online connection they managed. This means, it was not possible to relay mail through the mail server of one \NAME{ISP} while being online through the connection of another \NAME{ISP}. \masqmail\ is a solution to the wish of switching the relaying mail server easily.
meillo@391 325 \index{isp}
meillo@257 326
meillo@316 327 Related is \masqmail's ability to rewrite the sender's email address dependent on which \NAME{ISP} is used. This prevents mail from being likely classified as spam.
meillo@391 328 \index{spam}
meillo@257 329
meillo@369 330 To react on the different situations, \masqmail\ needs to query the current online state. Is an online connection available? And if it is: Which one? Three methods are implemented:
meillo@391 331 \index{online state}
meillo@238 332
meillo@369 333 \begin{enumerate}
meillo@391 334 \item Reading from a file
meillo@391 335 \item Reading the output of a command
meillo@391 336 \item Querying an \name{mserver} system
meillo@369 337 \end{enumerate}
meillo@391 338 \index{mserver}
meillo@238 339
meillo@374 340 Each method may return a string naming the route that is online or returning nothing to indicate offline state.
meillo@369 341
meillo@369 342
meillo@369 343 Mail for hosts inside the local network or for users on the local machine is not touched by this concept; such mail is always sent immediately.
meillo@238 344
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meillo@238 346
meillo@238 347
meillo@245 348
meillo@245 349
meillo@245 350
meillo@245 351
meillo@370 352 \section{Why \masqmail\ is worth it}
meillo@402 353 \index{masqmail}
meillo@245 354
meillo@369 355 First of all, \masqmail\ is better suited for its target field of operation (multiple non-permanent online connections) than every other \MTA. Especially is such usage easy to set up because \masqmail\ was designed for that. Many alternative \MTA{}s were not designed for those scenarios at all as the following two example show: ``Exim is designed for use on a network where most messages can be delivered at the first attempt.'' \cite[page~30]{hazel01}. ``qmail was designed for well-connected hosts: those with high-speed, always-on network connectivity.'' \cite[page9]{sill02}.
meillo@402 356 \index{non-permanent online connection}
meillo@391 357 \index{qmail}
meillo@391 358 \index{exim}
meillo@369 359
meillo@369 360 %fixme: hikernet
meillo@245 361
meillo@396 362 Additionally does \masqmail\ make it easy to run an \MTA\ on workstations or notebooks. There is no need to do complex configuration or to be a mail server expert. Only a handful of options need to be set; the host name, the local networks, and one route for relaying are sufficient in most times.
meillo@402 363 \index{masqmail!on notebooks}
meillo@402 364 \index{configuration}
meillo@245 365
meillo@369 366 Probably users say it best; in this case \person{Derek Broughton}:
meillo@391 367 \index{masqmail!users}
meillo@391 368
meillo@284 369 \begin{quote}
meillo@284 370 No kidding. The whole point is that you \_have\_ to have an \MTA\ and you don't
meillo@284 371 want to configure Postfix/Exim/Sendmail/Qmail (almost all of which I've
meillo@284 372 actually done).
meillo@284 373
meillo@369 374 I now use masqmail -- it's really simple, my configuration is all in debconf,
meillo@284 375 it's supported by whereami, and it's really simple :-)
meillo@284 376
meillo@284 377 I'm sure you can make any \MTA\ behave nicely when offline, but it was a chore
meillo@284 378 with all of them.
meillo@284 379 \hfill\citeweb[post~\#8]{ubuntuforums:simple-mailer}
meillo@284 380 \end{quote}
meillo@284 381
meillo@378 382 Not to forget \masqmail's size. \masqmail\ is much smaller than full-blown \MTA{}s like \sendmail, \postfix, or \exim, and still smaller than \qmail. (See section~\ref{sec:mta-comparison} for details.) This makes \masqmail\ a good choice for workstations or even embedded computers.
meillo@402 383 \index{qmail}
meillo@245 384
meillo@284 385 Again words of a user who chose \masqmail\ as \MTA\ on his old laptop with a 75 megahertz processor and eight megabytes of \NAME{RAM}:
meillo@391 386
meillo@284 387 \begin{quote}
meillo@284 388 Masqmail appears to be a great sendmail replacement in this case. It's small and is built to support sending mail ``off-line'', and to connecting to the \SMTP\ servers of several \NAME{ISP}s.
meillo@284 389 \hfill\citeweb{stosberg:low-mem-laptop}
meillo@284 390 \end{quote}
meillo@391 391 \index{isp}
meillo@402 392 \index{sendmail}
meillo@402 393 \index{masqmail!on notebooks}
meillo@92 394
meillo@92 395
meillo@92 396
meillo@370 397 Although the development on \masqmail\ has been stopped in 2003, \masqmail\ still has its users. Having users is already reason enough for further development and maintenance. This applies especially when the software covers a niche and when requirements for such software in general changed. Both is the case for \masqmail.
meillo@284 398
meillo@393 399 It is difficult to get numbers about users of Free Software because no one needs to tell anyone when he uses some software. \name{Debian}'s \name{popcon} statistics \citeweb{popcon.debian} are a try to provided numbers. For January 2009, the statistics report 60 \masqmail\ installations of which 49 are in active use. If it is assumed that one third of all \name{Debian} users report their installed software\footnote{One third is a high guess as it means there would be only about 230 thousand \name{Debian} installations in total. But according to the \name{Linux Counter} \citeweb{counter.li.org} between 490 thousand and 12 million \name{Debian} users can be estimated.}, there would be in total around 150 active \masqmail\ installations in \name{Debian}. \name{Ubuntu} which also does \name{popcon} statistics \citeweb{popcon.ubuntu}, counts 82 installations with 13 active ones. If here also one third of all systems submit their data, 40 active installations can be added. Including a guessed amount of additional 30 installations on other Unix operating systems makes about 220 \masqmail\ installations in total. Of course one person may have \masqmail\ installed on more than one computer, but a total of 150 different users seems to be realistic.
meillo@402 400 \index{Free Software}
meillo@391 401 \index{debian!popcon}
meillo@391 402 \index{masqmail!users}
meillo@402 403 \index{Linux Counter}
meillo@402 404 \index{Unix}
meillo@284 405
meillo@286 406 %The increasing number of systems using \masqmail, as it is shown on the \name{popcon} graph \citeweb{popcon.debian:masqmail}, seems to be impressive in the beginning as \masqmail\ was not developed during that time. But it might come from the increasing popularity of \name{popcon} over the time.
meillo@284 407
meillo@369 408 One thing became clear now: \masqmail\ has users. And software that is used should be developed and maintained.
meillo@92 409
meillo@92 410
meillo@275 411 % alternative: http://anfi.homeunix.org/sendmail/dialup10.html
meillo@96 412
meillo@275 413
meillo@175 414
meillo@96 415
meillo@96 416
meillo@245 417
meillo@245 418
meillo@245 419
meillo@245 420
meillo@92 421 \section{Problems to solve}
meillo@391 422 \index{masqmail!problems}
meillo@92 423
meillo@370 424 A program that is neglected for more than five years in a field of operation that changed during this time surely needs improvement. Security and spam have highly increased in importance since 2003. Dial-up connections became rare, instead broadband flat rates are common now. Other \MTA{}s evolved in respect to theses changes---\masqmail\ did not.
meillo@402 425 \index{dial-up}
meillo@96 426
meillo@369 427 The current market situation and trends for the future need to be identified. Looks at other \MTA{}s need to be taken. Required work on \masqmail\ needs to be defined in combination with the evaluation of strategies to do this work. And a plan for further development should be created.
meillo@96 428
meillo@96 429
meillo@245 430
meillo@245 431
meillo@245 432
meillo@245 433 \section{Delimitation}
meillo@96 434
meillo@369 435 This thesis is neither a installation guide for \masqmail\ nor a detailed explanation of \masqmail's source code. Installation and setup guides can be found on \masqmail's homepage \citeweb{masqmail:homepage}.
meillo@96 436
meillo@369 437 The \NAME{POP3} functionality of \masqmail\ receives few regard in this document because it is not directly related to the core of \masqmail\ which is being an \MTA.
meillo@391 438 \index{pop3}
meillo@96 439
meillo@369 440 The \name{mserver} system to query the online state is also only mentioned but not regarded further. It seems best to move this functionality into a separate program which is run through the shell command interface, anyway.
meillo@391 441 \index{mserver}
meillo@96 442
meillo@150 443
meillo@369 444