1.1 --- a/thesis/tex/1-Introduction.tex	Wed Jan 21 14:48:58 2009 +0100
     1.2 +++ b/thesis/tex/1-Introduction.tex	Wed Jan 21 15:19:25 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 explaination 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 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.
     1.9  
    1.10  
    1.11  
    1.12 @@ -9,24 +9,24 @@
    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 Engeneering 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 expected 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'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.
    1.25 +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.
    1.26  
    1.27  \begin{description}
    1.28  \item[\MTA:]
    1.29 -\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}.
    1.30 +\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}.
    1.31  
    1.32  \item[\NAME{MUA}:]
    1.33  \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}.
    1.34  
    1.35  \item[\NAME{MDA}:]
    1.36 -\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.
    1.37 +\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.
    1.38  \end{description}
    1.39  
    1.40  \begin{figure}
    1.41 @@ -44,13 +44,13 @@
    1.42  
    1.43  \subsubsection{Mail transfer with SMTP}
    1.44  
    1.45 -Today most of the email is transfered 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}.
    1.46 +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}.
    1.47  
    1.48  A selection of important concepts of \SMTP\ is explained here.
    1.49  
    1.50  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.
    1.51  
    1.52 -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 transfered 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 transfered and if the transfer was successful, the responsibility for the message is transfered as well. The responsibility chain ends at a user's mailbox, where he himself has control on the message.
    1.53 +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.
    1.54  
    1.55  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.
    1.56  
    1.57 @@ -62,7 +62,7 @@
    1.58  
    1.59  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.
    1.60  
    1.61 -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 convertion automatically in \NAME{MUA}s.
    1.62 +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.
    1.63  
    1.64  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.
    1.65  
    1.66 @@ -88,7 +88,7 @@
    1.67  
    1.68  \masqmail\ is covered by the \name{General Public License} (short: \GPL), which qualifies it as \freesw.
    1.69  
    1.70 -\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.
    1.71 +\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.
    1.72  
    1.73  The program's new homepage \citeweb{masqmail:homepage} is a collection of available information about this \MTA.
    1.74  
    1.75 @@ -103,16 +103,16 @@
    1.76  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.
    1.77  \hfill\citeweb{masqmail:homepage2}
    1.78  \end{quote}
    1.79 -It is inteded to cover a specific niche: non-permanent internet connection and different \NAME{ISP}s.
    1.80 +It is intended to cover a specific niche: non-permanent Internet connection and different \NAME{ISP}s.
    1.81  
    1.82  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:
    1.83  \begin{quote}
    1.84  In these cases, MasqMail is a slim replacement for full-blown MTAs such as sendmail, exim, qmail or postfix.
    1.85  \hfill\citeweb{packages.debian:masqmail}
    1.86  \end{quote}
    1.87 -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.
    1.88 +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.
    1.89  
    1.90 -\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''?
    1.91 +\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 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''?
    1.92  
    1.93  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.
    1.94  
    1.95 @@ -122,7 +122,7 @@
    1.96  
    1.97  \subsubsection*{Typical usage scenarios}
    1.98  
    1.99 -This section describes three common setups that makes senseful use of \masqmail. The first two are shown in figure \ref{fig:masqmail-typical-usage}.
   1.100 +This section describes three common setups that makes sensible use of \masqmail. The first two are shown in figure \ref{fig:masqmail-typical-usage}.
   1.101  
   1.102  \begin{figure}
   1.103  	\begin{center}
   1.104 @@ -136,14 +136,14 @@
   1.105  
   1.106  \begin{description}
   1.107  \item[Scenario 1:]
   1.108 -If no server is present, 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.
   1.109 +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, except different host names.
   1.110  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.
   1.111  
   1.112  \item[Scenario 2:]
   1.113 -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 using the \NAME{POP3} or \NAME{IMAP} protocol to fetch the mail in the server's mailbox from the workstations. Mail transfer from the \NAME{ISP} to the local server needs \NAME{POP3} or \NAME{IMAP} as well.
   1.114 +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 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, it can be solved by mounting the users mailbox from the server to the workstation, or by using the \NAME{POP3} or \NAME{IMAP} protocol to fetch the mail in the server's mailbox from the workstations. Mail transfer from the \NAME{ISP} to the local server needs \NAME{POP3} or \NAME{IMAP} as well.
   1.115  
   1.116  \item[Scenario 3:]
   1.117 -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 gets more and more common. Different networks have different setups: In one network it is best to send mail to an \NAME{ISP} for relay. In another network it might be prefered 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.
   1.118 +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 gets more and more common. Different networks have 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.
   1.119  \end{description}
   1.120  
   1.121  
   1.122 @@ -163,7 +163,7 @@
   1.123  \hfill\citeweb{masqmail:homepage2}
   1.124  \end{quote}
   1.125  
   1.126 -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. \masqmail\ should not be used for permanent internet connections. Or at least it needs to be secured with care.
   1.127 +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. \masqmail\ should not be used for permanent Internet connections. Or at least it needs to be secured with care.
   1.128  
   1.129  The Internet is the common example for an untrusted network, but this applies to any other untrusted network too.
   1.130  
   1.131 @@ -227,7 +227,7 @@
   1.132  
   1.133  The background of this concept was the send mail to the Internet while using one of a set of dial-up Internet connection from different \NAME{ISP}s. It was quite common that \NAME{ISP}s accepted mail for relay only if it came over a connection they managed. This means, one was not able to relay mail over the mail server of \NAME{ISP}\,1 while being online over the connection of \NAME{ISP}\,2. \masqmail\ is a solution to the wish of switching the relaying mail server easily.
   1.134  
   1.135 -Related is \masqmail's ability to rewrite the send's email address dependent on which \NAME{ISP} is used. This prevents mail from being likely classified as spam.
   1.136 +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.
   1.137  
   1.138  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: (1) Reading from a file, (2) reading the output of a command, and (3) by asking an \name{mserver} system. Each method may return a string naming the routes that is online or returning nothing to indicate offline state.
   1.139  
   1.140 @@ -245,7 +245,7 @@
   1.141  
   1.142  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.
   1.143  
   1.144 -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 hostname, the local networks, and one route for relaying are sufficient in most times. %fixme: is that true?
   1.145 +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. %fixme: is that true?
   1.146  
   1.147  Probably users say it best. In this case \person{Derek Broughton}:
   1.148  \begin{quote}
   1.149 @@ -271,7 +271,7 @@
   1.150  
   1.151  
   1.152  
   1.153 -Although development on \masqmail\ stopped in 2003 it still has its users. Having users is alone reason enough for futher development and maintenance. This applies especially if the software covers a niche and if requirements for such software in general change. Both matches in \masqmail's case.
   1.154 +Although development on \masqmail\ stopped in 2003 it still has its users. Having users is alone reason enough for further development and maintenance. This applies especially if the software covers a niche and if requirements for such software in general change. Both matches in \masqmail's case.
   1.155  
   1.156  It is difficult to get numbers about users of Free Software, because no one needs to tell anyone when he uses some software. \debian's \name{popcon} statistics \citeweb{popcon.debian} are a try to provided numbers. The statistics report 60 \masqmail\ installations of which 49 are in active use, for January 2009. If it is assumed that one third of all \debian\ users report their installed software\footnote{One third is a high guess as it means there would be only about 230 thousand \debian\ installations in total. But according to the \name{Linux Counter} \citeweb{counter.li.org} between 490 thousand and 12 million \debian\ users can be estimated.}, there would be in total around 150 active \masqmail\ installations in \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.
   1.157  
   1.158 @@ -293,7 +293,7 @@
   1.159  
   1.160  \section{Problems to solve}
   1.161  
   1.162 -A program, that no one has developed further for nearly six years, that is located in a field of operation that changed during that time, surely needs improvement. Security and spam have now highly increased importance compared to 2003. Dial-up connections became rare---broadband flatrates are common now. Other \MTA{}s evolved in respect to theses changes, \masqmail\ did not.
   1.163 +A program, that no one has developed further for nearly six years, that is located in a field of operation that changed during that time, surely needs improvement. Security and spam have now highly increased importance compared to 2003. Dial-up connections became rare---broadband flat rates are common now. Other \MTA{}s evolved in respect to theses changes, \masqmail\ did not.
   1.164  
   1.165  The current and trends for a future market situation needs to be identified. Looks at other \MTA{}s need to be taken. And required work on \masqmail\ needs to be defined in combination with the evaluation of strategies to do this work. Finally a plan for further development should be created.
   1.166  
   1.167 @@ -303,7 +303,7 @@
   1.168  
   1.169  \section{Delimitation}
   1.170  
   1.171 -This thesis is neigher a installation guide for \masqmail\ nor a bit by bit explanation of \masqmail's source code. Installation and setup guides can be found on \masqmail's homepage \citeweb{masqmail:homepage}.
   1.172 +This thesis is neither a installation guide for \masqmail\ nor a bit by bit explanation of \masqmail's source code. Installation and setup guides can be found on \masqmail's homepage \citeweb{masqmail:homepage}.
   1.173  
   1.174  Also not regarded is the \NAME{POP3} functionality of \masqmail.
   1.175