1.1 --- a/thesis/tex/1-Introduction.tex	Wed Jan 14 12:28:06 2009 +0100
     1.2 +++ b/thesis/tex/1-Introduction.tex	Wed Jan 14 12:31:52 2009 +0100
     1.3 @@ -17,15 +17,13 @@
     1.4  
     1.5  \subsubsection{Mail agents}
     1.6  
     1.7 -This thesis will frequently use the three terms: \MTA, \NAME{MUA}, and \NAME{MDA}. The name the three different kinds of software on which the email system depends. Here they are explained with references to the snail mail system one knows from everyday's life. Figure \ref{fig:mail-agents} shows the relation between them and the way an email message takes trough the system.
     1.8 +This thesis will frequently use the three terms: \MTA, \NAME{MUA}, and \NAME{MDA}. The name the three different kinds of software that are the nodes of the email infrastructure. Here they are explained with references to the snail mail system which is known from everyday's life. Figure \ref{fig:mail-agents} shows the relation between those three mail agents and the way an email message takes trough the system.
     1.9  
    1.10  \paragraph{MTA}
    1.11 -\name{Mail Tranfer Agents} are for electronic mail what post offices are for snail mail. The basic job of an \MTA\ is to transport mail from senders to recipients, or more pedantic: from \MTA\ to \MTA. 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}. \MTA{}s are explained in more detail in chapter \ref{chap:mail-transfer-agents}.
    1.12 -
    1.13 +\name{Mail Tranfer 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}.
    1.14  
    1.15  \paragraph{MUA}
    1.16 -\name{Mail User Agents} are the software the user deals with. He writes and reads email with it. The \NAME{MUA} passes outgoing mail to the nearest \MTA, and the \NAME{MUA} displays the contents of the user's mailbox. Well known \NAME{MUA}s are \name{Mozilla Thunderbird} and \name{mutt} on \unix\ systems, and \name{Microsoft Outlook} on \name{Windows}.
    1.17 -
    1.18 +\name{Mail User Agents} are the software the user deals with. He writes and reads email with it. The \NAME{MUA} passes outgoing mail to the nearest \MTA. Also the \NAME{MUA} displays the contents of the user's mailbox. Well known \NAME{MUA}s are \name{Mozilla Thunderbird} and \name{mutt} on \unix\ systems, and \name{Microsoft Outlook} on \name{Windows}.
    1.19  
    1.20  \paragraph{MDA}
    1.21  \name{Mail Delivery Agents} correspond to postmen in the real world. They receive mail, destinated to recipients they are responsible for, from an \MTA, and deliver it to the mailboxes of those recipients. Many \MTA{}s include an own \NAME{MDA}, but specialized ones exist: \name{procmail} and \name{maildrop} are examples.
    1.22 @@ -67,11 +65,15 @@
    1.23  
    1.24  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.
    1.25  
    1.26 +\begin{quote}
    1.27  \input{input/sample-email.txt}
    1.28 +\end{quote}
    1.29  
    1.30 -Email messages are put into envelopes for transfer. This concept is derived from the real world, so it is easy to understand. The envelope is what 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 by using mail header data. The user has not to deal with them.
    1.31 +Email messages are put into envelopes for transfer. This concept is 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 by using mail header data. The user has not to deal with them.
    1.32  
    1.33 -The sample message would 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. There is no difference to how it would be done for snail mail.
    1.34 +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.
    1.35 +
    1.36 +The sample message would 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.
    1.37  
    1.38  
    1.39  
    1.40 @@ -81,15 +83,15 @@
    1.41  \section{The \masqmail\ project}
    1.42  \label{sec:masqmail}
    1.43  
    1.44 -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.
    1.45 +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. Throughout the next four years, he worked steadily on it, releasing new versions every few weeks. In total it were 53 releases, which is in average a new version every 20 days.
    1.46  
    1.47 -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}.
    1.48 +This thesis bases on the latest release of \masqmail---version 0.2.21 from November 2005. It was released after a 28 month gap. The source code of 0.2.21 is the same as of 0.2.20, only build documents were modified. The release tarball can be retrieved from the \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{debian:packages}. Probably was only put into public in the \debian\ pool because \masqmail's homepage \citeweb{masqmail:homepage2} does not include it.
    1.49  
    1.50  \masqmail\ is covered by the \name{General Public License} (short: \GPL), which qualifies it as \freesw.
    1.51  
    1.52  \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.
    1.53  
    1.54 -The program's new homepage is a collection of available information about this \MTA\ \citeweb{masqmail:homepage}.
    1.55 +The program's new homepage \citeweb{masqmail:homepage} is a collection of available information about this \MTA.
    1.56  
    1.57  
    1.58  
    1.59 @@ -118,20 +120,18 @@
    1.60  
    1.61  
    1.62  
    1.63 -\subsubsection*{A typical usage scenario}
    1.64 +\subsubsection*{Typical usage scenarios}
    1.65  
    1.66 -This section describes two common setups that makes senseful use of \masqmail.
    1.67 +This section describes two common setups that makes senseful use of \masqmail. They are shown in figure \ref{fig:masqmail-typical-usage}.
    1.68  
    1.69 -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.
    1.70 +\paragraph{Scenario 1}
    1.71 +Imagine a home network consisting of some workstations without a server. The network is connected to the Internet.
    1.72  
    1.73 -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.
    1.74 +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. The configuration of \masqmail\ would be the same on every computer, except different hostnames.
    1.75 +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. % pop3/imap
    1.76  
    1.77 -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.
    1.78 -
    1.79 -%fixme: what about notebooks?
    1.80 -<< notebooks >>
    1.81 -
    1.82 -Figure \ref{fig:masqmail-typical-usage} despicts the two scenarios.
    1.83 +\paragraph{Scenario 2}
    1.84 +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, dependent on the desination 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, it can be solved by mounting the users mailbox from the server to the workstation, or by making the workstations fetch mail from the server. % pop3/imap
    1.85  
    1.86  \begin{figure}
    1.87  	\begin{center}
    1.88 @@ -141,23 +141,26 @@
    1.89  	\label{fig:masqmail-typical-usage}
    1.90  \end{figure}
    1.91  
    1.92 -In general, all kinds of usage scenarios within a trusted network are possible.
    1.93 +%fixme: what about notebooks?
    1.94 +<< notebooks >>
    1.95 +
    1.96 +In general, all kinds of usage scenarios within a trusted network are possible. Important to notice is that mail can not be send from outside into the local network. This limitation leads to the next section.
    1.97  
    1.98  
    1.99  
   1.100  
   1.101  \subsubsection*{Limitations}
   1.102  
   1.103 -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.
   1.104 +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 are not as needed for such usage.
   1.105  
   1.106 -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:
   1.107 +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:
   1.108  
   1.109  \begin{quote}
   1.110  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.
   1.111  \hfill\citeweb{masqmail:homepage2}
   1.112  \end{quote}
   1.113  
   1.114 -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.
   1.115 +The actual problem is not the permanent Internet connection, but listening for incomming mail on it. If a firewall is closed for incoming mail, then the permanent Internet connection is no problem.
   1.116  
   1.117  Hence, \masqmail\ should not be used for permanent internet connections. Or at least it needs to be secured with care.
   1.118  
   1.119 @@ -183,22 +186,30 @@
   1.120  
   1.121  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.
   1.122  
   1.123 -With \masqmail\ comes the small tool \path{mservdetect}; it helps setting up a configuration that uses the \name{mserver} system to detect the online state. Two other binaries get compiled for testing purposes: \path{readtest} and \path{smtpsend}. All three programs use \masqmail\ source code; they only add a file with a \verb+main()+ function each.
   1.124 +Some functionality of \masqmail\ 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.
   1.125 +
   1.126 +With \masqmail\ comes the small tool \path{mservdetect}; it helps setting up a configuration that uses the \name{mserver} system to detect the online state. Two other binaries get compiled for testing purposes: \path{readtest} and \path{smtpsend}. All three programs use parts of \masqmail's source code; they only add a file with a \verb+main()+ function each.
   1.127  
   1.128  
   1.129  
   1.130  \subsubsection*{Features}
   1.131  \label{sec:masqmail-features}
   1.132  
   1.133 -\masqmail\ supports two channels for incoming mail: (1) Standard input, used when \path{masqmail} is executed on the command line and (2) a \NAME{TCP} socket, used by local or remote clients that talk \SMTP. The outgoing channels for mail are: (1) direct delivery to local mailboxes (in \name{mbox} or \name{maildir} format), (2) local pipes to pass mail to a program (e.g.\ gateways to \NAME{UUCP}, gateways to fax, or \NAME{MDA}s), and (3) \NAME{TCP} sockets to transfer mail to other \MTA{}s using the \SMTP\ protocol.
   1.134 +\masqmail\ supports two channels for incoming mail: (1) Standard input, used when \path{masqmail} is executed on the command line and (2) a \NAME{TCP} socket, used by local or remote clients that talk \SMTP. The outgoing channels for mail are: (1) direct delivery to local mailboxes (in \name{mbox} or \name{maildir} format), (2) local pipes to pass mail to a program (e.g.\ gateways to \NAME{UUCP}, gateways to fax, or \NAME{MDA}s), and (3) \NAME{TCP} sockets to transfer mail to other \MTA{}s using the \SMTP\ protocol. Figure \ref{fig:masqmail-channels} shows this as a picture. (The ``online state'' input is explained a bit later.)
   1.135 +
   1.136 +\begin{figure}
   1.137 +	\begin{center}
   1.138 +		\includegraphics[scale=0.75]{img/masqmail-channels.eps}
   1.139 +	\end{center}
   1.140 +	\caption{Incoming and outgoing channels of \masqmail}
   1.141 +	\label{fig:masqmail-channels}
   1.142 +\end{figure}
   1.143  
   1.144  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}.
   1.145  
   1.146  Mail queuing and alias expansion is both supported.
   1.147  
   1.148 -\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 to determine if some message is allowed to be sent over it. This concept is explained in section \ref{sec:masqmail-routes} in detail. Mail to destinations outside the local network gets queued until an online connections is available.
   1.149 -
   1.150 -The \masqmail\ executable can be called under various names for sendmail-compatibility reasons. This is organized by symbolic links with different names pointing to the \masqmail\ executable. The \sendmail\ names are \path{/usr/lib/sendmail} and \path{/usr/sbin/sendmail} because many programs expect the \mta\ to be located there. Further more \sendmail\ supports calling it with a different name instead of supplying command line arguments. The best known of this 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 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 other software needing it.} \path{hoststat} and \path{purgestat} are missing for complete sendmail-compatibility.
   1.151 +The \masqmail\ executable can be called under various names for sendmail-compatibility reasons (see section \ref{sec:sendmail-compat}). This is organized by symbolic links with different names pointing to the \masqmail\ executable. The \sendmail\ names are \path{/usr/lib/sendmail} and \path{/usr/sbin/sendmail} because many programs expect the \mta\ to be located there. Further more \sendmail\ supports calling it with a different name instead of supplying command line arguments. The best known of this 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 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 other software needing it.} \path{hoststat} and \path{purgestat} are missing for complete sendmail-compatibility.
   1.152  %masqmail: mailq, mailrm, runq, rmail, smtpd/in.smtpd
   1.153  %sendmail: hoststat, mailq, newaliases, purgestat, smtpd
   1.154  
   1.155 @@ -209,6 +220,8 @@
   1.156  \subsubsection*{Online detection and routes}
   1.157  \label{sec:masqmail-routes}
   1.158  
   1.159 +\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 to determine if some message is allowed to be sent over it. This concept is explained in section \ref{sec:masqmail-routes} in detail. Mail to destinations outside the local network gets queued until an online connections is available.
   1.160 +
   1.161  \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.
   1.162  
   1.163  \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.
   1.164 @@ -269,6 +282,7 @@
   1.165  
   1.166  << limit against stuff not covered here >>
   1.167  
   1.168 +pop3 stuff of masqmail is not regarded.
   1.169  
   1.170  
   1.171