1.1 --- a/thesis/tex/1-Introduction.tex	Wed Jan 28 16:49:45 2009 +0100
     1.2 +++ b/thesis/tex/1-Introduction.tex	Fri Jan 30 21:20:00 2009 +0100
     1.3 @@ -1,7 +1,7 @@
     1.4  \chapter{Introduction}
     1.5  \label{chap:introduction}
     1.6  
     1.7 -This chapter first introduces some basic email concepts that are essential to understand the rest 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 worth, its problems are pointed out. These problems which are to solve are the topics that are covered throughout this thesis.
     1.8 +This chapter first introduces some basic email concepts that are essential for understanding the rest 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 worth, its problems are pointed out. These problems which are to solve are the topics that are covered throughout this thesis.
     1.9  
    1.10  
    1.11  
    1.12 @@ -9,14 +9,14 @@
    1.13  
    1.14  \section{Email prerequisites}
    1.15  
    1.16 -Electronic mail is a service on the Internet and thus, like other Internet services, defined and standardized by \RFC{}s under management of the \name{Internet Engineering Task Force} (short: \NAME{IETF}). \RFC{}s are highly technical documents and it is not expected that the readers of this thesis are familiar with them.
    1.17 +Electronic mail is a service on the Internet and thus, like other Internet services, defined and standardized by \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.
    1.18  
    1.19  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. They are assumed to be known in the rest of the thesis.
    1.20  
    1.21  
    1.22  \subsubsection{Mail agents}
    1.23  
    1.24 -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 life. Figure \ref{fig:mail-agents} shows the relation between those three mail agents and the way an email message takes trough the system.
    1.25 +This thesis will frequently use the three terms: \MTA, \NAME{MUA}, and \NAME{MDA}. They 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 life. Figure \ref{fig:mail-agents} shows the relation between those three mail agents and the way an email message takes trough the system.
    1.26  
    1.27  \begin{description}
    1.28  \item[\MTA:]
    1.29 @@ -26,7 +26,7 @@
    1.30  \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}.
    1.31  
    1.32  \item[\NAME{MDA}:]
    1.33 -\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 \NAME{MDA}, but specialized ones exist: \name{procmail} and \name{maildrop} are examples.
    1.34 +\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 \NAME{MDA}, but independent ones exist: \name{procmail} and \name{maildrop} are examples.
    1.35  \end{description}
    1.36  
    1.37  \begin{figure}
    1.38 @@ -44,23 +44,23 @@
    1.39  
    1.40  \subsubsection{Mail transfer with SMTP}
    1.41  
    1.42 -Today most of the email is transferred using the \name{Simple Mail Transfer Protocol} (short: \SMTP), which is defined in \RFC821 and the successors \RFC2821 and \RFC5321. A good entry point for further information is \citeweb{wikipedia:smtp}.
    1.43 +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}.
    1.44  
    1.45  A selection of important concepts of \SMTP\ is explained here.
    1.46  
    1.47  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 gets stored for some time on each \MTA, until it is forwarded to the next \MTA.
    1.48  
    1.49 -This leads to the concept of \name{responsibility}. A mail message is always in the responsibility of one system. First it is the \NAME{MUA}. After it was transferred to the first \MTA, it takes the responsibility for the message over. The \NAME{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 \NAME{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.
    1.50 +This leads to the concept of \name{responsibility}. A mail message is always in the responsibility of one system. First it is the \NAME{MUA}. When it is transferred to an \MTA, this \MTA\ takes over the responsibility for the message too. The \NAME{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 \NAME{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.
    1.51  
    1.52 -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.
    1.53 +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.
    1.54  
    1.55  
    1.56  
    1.57  \subsubsection{Mail messages}
    1.58  
    1.59 -Mail messages consist of text in a specific format. This format is specified in \RFC822, and the successors \RFC2822 and \RFC5322.
    1.60 +Mail messages consist of text in a specific format. This format is specified in \RFC\,822, and the successors \RFC\,2822 and \RFC\,5322.
    1.61  
    1.62 -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 address(es) of the recipient(s), the date, and possibly further information. Their order is irrelevant. Headers are named after the colon separated start of those lines, for example the ``\texttt{Date:}'' header. A user may write the header himself, but normally the \NAME{MUA} does this job.
    1.63 +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 \NAME{MUA} does this job.
    1.64  
    1.65  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 \NAME{MUA}s.
    1.66  
    1.67 @@ -68,7 +68,7 @@
    1.68  
    1.69  \codeinput{input/sample-email.txt}
    1.70  
    1.71 -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.
    1.72 +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.
    1.73  
    1.74  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.
    1.75  
    1.76 @@ -82,32 +82,32 @@
    1.77  \section{The \masqmail\ project}
    1.78  \label{sec:masqmail}
    1.79  
    1.80 -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.
    1.81 +The \masqmail\ project was started 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.
    1.82  
    1.83 -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{packages.debian}. Probably was only put into public in the \debian\ pool because \masqmail's homepage \citeweb{masqmail:homepage2} does not include it.
    1.84 +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{packages.debian}. It seems as if this version was only put into public there because \masqmail's homepage \citeweb{masqmail:homepage2} does not include it.
    1.85  
    1.86 -\masqmail\ is covered by the \name{General Public License} (short: \NAME{GPL}), which qualifies it as \freesw.
    1.87 +\masqmail\ is covered by the \name{General Public License} (short: \NAME{GPL}) which qualifies it as \freesw.
    1.88  
    1.89 -\person{Kurth} abandoned \masqmail\ after 2005, and no one adopted 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.
    1.90 +\person{Kurth} abandoned \masqmail\ after 2005 and no one adopted 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.
    1.91  
    1.92  The program's new homepage \citeweb{masqmail:homepage} is a collection of available information about this \MTA.
    1.93  
    1.94  
    1.95  
    1.96  
    1.97 -\subsection{Target field of \masqmail}
    1.98 +\subsection{Target field}
    1.99  \label{sec:masqmail-target-field}
   1.100  
   1.101  The intention \person{Kurth} had when creating \masqmail\ is best told in his own words:
   1.102  \begin{quote}
   1.103 -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.
   1.104 +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.
   1.105  \hfill\citeweb{masqmail:homepage2}
   1.106  \end{quote}
   1.107 -It is intended to cover a specific niche: non-permanent Internet connection and different \NAME{ISP}s.
   1.108 +It is intended to cover a specific niche: non-permanent Internet connection and different \name{Internet Service Providers} (short: \NAME{ISP}s).
   1.109  
   1.110 -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:
   1.111 +Although it can basically replace other \MTA{}s it is not \emph{generally} aimed to do so. The package description of \masqmail\ within \debian\ states this more clearly by changing the last sentence to:
   1.112  \begin{quote}
   1.113 -In these cases, MasqMail is a slim replacement for full-blown MTAs such as sendmail, exim, qmail or postfix.
   1.114 +In these cases, MasqMail is a slim replacement for full-blown \MTA{}s such as sendmail, exim, qmail or postfix.
   1.115  \hfill\citeweb{packages.debian:masqmail}
   1.116  \end{quote}
   1.117  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 accessible from untrusted locations.