1.1 --- a/thesis/tex/0-preface.tex	Wed Jan 21 14:48:58 2009 +0100
     1.2 +++ b/thesis/tex/0-preface.tex	Wed Jan 21 15:19:25 2009 +0100
     1.3 @@ -16,7 +16,7 @@
     1.4  
     1.5  << make the topic more concrete and limit it >> %FIXME
     1.6  
     1.7 -<< have text by oliver here? >> %TODO
     1.8 +<< have text by Oliver here? >> %TODO
     1.9  
    1.10  usage examples:
    1.11  
    1.12 @@ -36,7 +36,7 @@
    1.13  
    1.14  This work focuses on the \unix\ operating system.
    1.15  Experience in usage, administration and program development is assumed.
    1.16 -This includes the basic toolchain (e.g.\ \name{tar}, \name{grep}, etc.), user, file and permission management, as well as writing, compiling and installing programs written in the C language.
    1.17 +This includes the basic tool chain (e.g.\ \name{tar}, \name{grep}, etc.), user, file and permission management, as well as writing, compiling and installing programs written in the C language.
    1.18  
    1.19  General information about \unix\ can be found in \cite{kernighan84} %FIXME: references
    1.20  . %FIXME: references
    1.21 @@ -45,9 +45,9 @@
    1.22  
    1.23  
    1.24  
    1.25 -\section*{Organisation}
    1.26 +\section*{Organization}
    1.27  
    1.28 -<< write about organisation of the book: parts, chapters, sections. And more thats useful to know. >> %FIXME
    1.29 +<< write about organization of the book: parts, chapters, sections. And more that's useful to know. >> %FIXME
    1.30  
    1.31  << explain where the main part lies (theory vs. implementation) >> %FIXME:
    1.32  
    1.33 @@ -58,17 +58,17 @@
    1.34  The following typographic conventions are used in this thesis:
    1.35  
    1.36  \begin{enumerate}
    1.37 -\item \emph{Italic shape} is used to emphasize text, to introduce new terma, and for names, including product, host, and user names, as well as email addresses.
    1.38 +\item \emph{Italic shape} is used to emphasize text, to introduce new terms, and for names, including product, host, and user names, as well as email addresses.
    1.39  
    1.40  \item For names of persons \textsc{Small Caps} are used.
    1.41  
    1.42 -\item File and path names, source code excrepts, contents of files, and output from programs are displayed in \texttt{Typewriter font}.
    1.43 +\item File and path names, source code excerpts, contents of files, and output from programs are displayed in \texttt{Typewriter font}.
    1.44  \end{enumerate}
    1.45  
    1.46  References to external resources are marked using one of three styles, distinguished by the type of resource.
    1.47  
    1.48  \begin{enumerate}
    1.49 -\item References to books, articles, and similar documents looks like this: \cite{kernighan84}. The letters represent the author(s) (here \person{Kenighan} and \person{Pike}), the number represents the year of publication (here 1984).
    1.50 +\item References to books, articles, and similar documents looks like this: \cite{kernighan84}. The letters represent the author(s) (here \person{Kernighan} and \person{Pike}), the number represents the year of publication (here 1984).
    1.51  
    1.52  \item Websites differ from documents as they are less of a text written by some author but more a place where information is gathered. They are only indicated by numbers, like for example: \citeweb{masqmail:homepage}.
    1.53  

     2.1 --- a/thesis/tex/1-Introduction.tex	Wed Jan 21 14:48:58 2009 +0100
     2.2 +++ b/thesis/tex/1-Introduction.tex	Wed Jan 21 15:19:25 2009 +0100
     2.3 @@ -1,7 +1,7 @@
     2.4  \chapter{Introduction}
     2.5  \label{chap:introduction}
     2.6  
     2.7 -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.
     2.8 +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.
     2.9  
    2.10  
    2.11  
    2.12 @@ -9,24 +9,24 @@
    2.13  
    2.14  \section{Email prerequisites}
    2.15  
    2.16 -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.
    2.17 +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.
    2.18  
    2.19  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.
    2.20  
    2.21  
    2.22  \subsubsection{Mail agents}
    2.23  
    2.24 -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.
    2.25 +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.
    2.26  
    2.27  \begin{description}
    2.28  \item[\MTA:]
    2.29 -\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}.
    2.30 +\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}.
    2.31  
    2.32  \item[\NAME{MUA}:]
    2.33  \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}.
    2.34  
    2.35  \item[\NAME{MDA}:]
    2.36 -\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.
    2.37 +\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.
    2.38  \end{description}
    2.39  
    2.40  \begin{figure}
    2.41 @@ -44,13 +44,13 @@
    2.42  
    2.43  \subsubsection{Mail transfer with SMTP}
    2.44  
    2.45 -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}.
    2.46 +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}.
    2.47  
    2.48  A selection of important concepts of \SMTP\ is explained here.
    2.49  
    2.50  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.
    2.51  
    2.52 -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.
    2.53 +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.
    2.54  
    2.55  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.
    2.56  
    2.57 @@ -62,7 +62,7 @@
    2.58  
    2.59  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.
    2.60  
    2.61 -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.
    2.62 +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.
    2.63  
    2.64  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.
    2.65  
    2.66 @@ -88,7 +88,7 @@
    2.67  
    2.68  \masqmail\ is covered by the \name{General Public License} (short: \GPL), which qualifies it as \freesw.
    2.69  
    2.70 -\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.
    2.71 +\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.
    2.72  
    2.73  The program's new homepage \citeweb{masqmail:homepage} is a collection of available information about this \MTA.
    2.74  
    2.75 @@ -103,16 +103,16 @@
    2.76  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.
    2.77  \hfill\citeweb{masqmail:homepage2}
    2.78  \end{quote}
    2.79 -It is inteded to cover a specific niche: non-permanent internet connection and different \NAME{ISP}s.
    2.80 +It is intended to cover a specific niche: non-permanent Internet connection and different \NAME{ISP}s.
    2.81  
    2.82  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:
    2.83  \begin{quote}
    2.84  In these cases, MasqMail is a slim replacement for full-blown MTAs such as sendmail, exim, qmail or postfix.
    2.85  \hfill\citeweb{packages.debian:masqmail}
    2.86  \end{quote}
    2.87 -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.
    2.88 +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.
    2.89  
    2.90 -\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''?
    2.91 +\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''?
    2.92  
    2.93  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.
    2.94  
    2.95 @@ -122,7 +122,7 @@
    2.96  
    2.97  \subsubsection*{Typical usage scenarios}
    2.98  
    2.99 -This section describes three common setups that makes senseful use of \masqmail. The first two are shown in figure \ref{fig:masqmail-typical-usage}.
   2.100 +This section describes three common setups that makes sensible use of \masqmail. The first two are shown in figure \ref{fig:masqmail-typical-usage}.
   2.101  
   2.102  \begin{figure}
   2.103  	\begin{center}
   2.104 @@ -136,14 +136,14 @@
   2.105  
   2.106  \begin{description}
   2.107  \item[Scenario 1:]
   2.108 -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.
   2.109 +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.
   2.110  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.
   2.111  
   2.112  \item[Scenario 2:]
   2.113 -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.
   2.114 +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.
   2.115  
   2.116  \item[Scenario 3:]
   2.117 -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.
   2.118 +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.
   2.119  \end{description}
   2.120  
   2.121  
   2.122 @@ -163,7 +163,7 @@
   2.123  \hfill\citeweb{masqmail:homepage2}
   2.124  \end{quote}
   2.125  
   2.126 -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.
   2.127 +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.
   2.128  
   2.129  The Internet is the common example for an untrusted network, but this applies to any other untrusted network too.
   2.130  
   2.131 @@ -227,7 +227,7 @@
   2.132  
   2.133  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.
   2.134  
   2.135 -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.
   2.136 +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.
   2.137  
   2.138  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.
   2.139  
   2.140 @@ -245,7 +245,7 @@
   2.141  
   2.142  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.
   2.143  
   2.144 -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?
   2.145 +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?
   2.146  
   2.147  Probably users say it best. In this case \person{Derek Broughton}:
   2.148  \begin{quote}
   2.149 @@ -271,7 +271,7 @@
   2.150  
   2.151  
   2.152  
   2.153 -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.
   2.154 +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.
   2.155  
   2.156  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.
   2.157  
   2.158 @@ -293,7 +293,7 @@
   2.159  
   2.160  \section{Problems to solve}
   2.161  
   2.162 -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.
   2.163 +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.
   2.164  
   2.165  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.
   2.166  
   2.167 @@ -303,7 +303,7 @@
   2.168  
   2.169  \section{Delimitation}
   2.170  
   2.171 -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}.
   2.172 +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}.
   2.173  
   2.174  Also not regarded is the \NAME{POP3} functionality of \masqmail.
   2.175  

     3.1 --- a/thesis/tex/2-MarketAnalysis.tex	Wed Jan 21 14:48:58 2009 +0100
     3.2 +++ b/thesis/tex/2-MarketAnalysis.tex	Wed Jan 21 15:19:25 2009 +0100
     3.3 @@ -101,7 +101,7 @@
     3.4  
     3.5  \subsubsection*{Unified Messaging}
     3.6  \label{sec:unified-messaging}
     3.7 -\name{Unified messaging}, although often used exchangeable with unified communications, is only a subset of it. It does not require real-time data transmission and is therefore only usable for asynchronous communication \citeweb{wikipedia:uc}. Unified messaging's function is basically: Receiving incoming messages from various channels, converting them into a common format, and storing them into a single memory. The stored messages can then be accessed from different devices \citeweb{wikipedia:um}.
     3.8 +\name{Unified messaging}, although often used exchangeable with unified communications, is only a subset of it. It does not require real-time data transmission and is therefore only usable for asynchronous communication \citeweb{wikipedia:uc}. Unified Messaging's function is basically: Receiving incoming messages from various channels, converting them into a common format, and storing them into a single memory. The stored messages can then be accessed from different devices \citeweb{wikipedia:um}.
     3.9  
    3.10  The easiest way of Unified Messaging is to base it on either email and convert all input sources to email messages (as attachments for instance) and store them in the user's mail box, or use the telephone system as basis and convert text messages to speech. Both is technically possible for asynchronous communication.
    3.11  
    3.12 @@ -189,7 +189,7 @@
    3.13  \subsubsection*{Provider independence}
    3.14  Today's email structure is heavily dependent on email providers. This means, most people have email addresses from some provider. These can be providers that offer email accounts in addition to their regular services, for example online connections. \NAME{AOL} and \name{T\mbox{-}On\-line} for instance do so. Or specialized email providers that commonly offer free mail as well as enhanced mail services, one must pay for. Examples for email providers are \NAME{GMX}, \name{Yahoo}, and \name{Hotmail}.  %fixme: check for non-breakable dash
    3.15  
    3.16 -Outgoing mail is send either with the webmail client of the provider or using \name{mail user agent}s sending it to the provider for relay. Incoming mail is read with the webmail client or retrieved from the provider via \NAME{POP3} or \NAME{IMAP} to the local computer to be read using the \name{mail user agent}. This means all mail sending and receiving work is done by the provider.
    3.17 +Outgoing mail is send either with the web mail client of the provider or using \name{mail user agent}s sending it to the provider for relay. Incoming mail is read with the web mail client or retrieved from the provider via \NAME{POP3} or \NAME{IMAP} to the local computer to be read using the \name{mail user agent}. This means all mail sending and receiving work is done by the provider.
    3.18  
    3.19  The reason therefor is originated in the time when people used dial-up connections to the Internet. A mail server needs to be online to receive email. Sending mail is no problem, but receiving it is hardly possible with an \MTA\ being few time online. Internet service providers had servers running all day long connected to the Internet. So they offered email service, and they still do.
    3.20  

     4.1 --- a/thesis/tex/3-MailTransferAgents.tex	Wed Jan 21 14:48:58 2009 +0100
     4.2 +++ b/thesis/tex/3-MailTransferAgents.tex	Wed Jan 21 15:19:25 2009 +0100
     4.3 @@ -105,7 +105,7 @@
     4.4  	\label{tab:mta-market-share}
     4.5  \end{table}
     4.6  
     4.7 -All surveys show high market shares for the four \MTA{}s: \sendmail, \exim, \qmail, and \postfix. Only the \name{Microsoft} mail server software and \name{IMail} have comparable large shares. Other \freesw\ \mta{}s (\name{smail}, \name{zmailer}, \name{MMDF}, \name{courier-mta}) are less important and seldom used.
     4.8 +All surveys show high market shares for the four \MTA{}s: \sendmail, \exim, \qmail, and \postfix. Only the \name{Microsoft} mail server software and \name{IMail} have comparable large shares. Other \freesw\ \mta{}s (\name{smail}, \name{zmailer}, \NAME{MMDF}, \name{courier-mta}) are less important and seldom used.
     4.9  
    4.10  The three surveys base on different data. \person{Bernstein} took 1\,000\,000 randomly chosen \NAME{IP} addresses, containing 39\,206 valid hosts; 958 of them accepted \NAME{SMTP} connections. The \person{Simpson} and \person{Bekman} survey used only domains owned by companies; in total 400\,000 hosts. \name{MailRadar} scanned 2\,818\,895 servers, leading to 59\,209 accepted connections.
    4.11  
    4.12 @@ -187,7 +187,7 @@
    4.13  
    4.14  This section does not try to provide a throughout \MTA\ comparison, because this is already done by others. Remarkable comparisons are the one by \person{Dan Shearer} \cite{shearer06} and a discussion on the mailing list \name{plug@lists.q-linux.com} \cite{plug:mtas}. Tabular overviews may be found at \citeweb{mailsoftware42}, \citeweb{wikipedia:comparison-of-mail-servers}, and \cite[section 1.9]{lifewithqmail}.
    4.15  
    4.16 -Here provided is an overview important properties of the four previously introduced \MTA{}s. The data comes from the above stated sources and is collected in table \ref{tab:mta-comparison}\footnote{The lines of code were messured with \person{David~A.\ Wheeler}'s \name{sloccount} \citeweb{sloccount}.}.
    4.17 +Here provided is an overview important properties of the four previously introduced \MTA{}s. The data comes from the above stated sources and is collected in table \ref{tab:mta-comparison}\footnote{The lines of code were measured with \person{David~A.\ Wheeler}'s \name{sloccount} \citeweb{sloccount}.}.
    4.18  
    4.19  \begin{table}
    4.20  % FIXME: improve table data!!!

     5.1 --- a/thesis/tex/4-MasqmailsFuture.tex	Wed Jan 21 14:48:58 2009 +0100
     5.2 +++ b/thesis/tex/4-MasqmailsFuture.tex	Wed Jan 21 15:19:25 2009 +0100
     5.3 @@ -95,9 +95,9 @@
     5.4  \paragraph{\RF6: Authentication}
     5.5  One thing to avoid is being an \name{open relay}. Open relays allow to relay mail from everywhere to everywhere. This is a source of spam. The solution is restricting relay\footnote{Relaying is passing mail, that is not from and not for the own system, through it.} access. It may be also wanted to refuse all connections to the \MTA\ except ones from a specific set of hosts.
     5.6  
     5.7 -Several ways to restrict access are available. The most simple one is restriction by the \NAME{IP} address. No extra complexity is added this way, but the \NAME{IP} addresses have to be static or within known ranges. This approach is often used to allow relaying for local nets. The access check can be done by the \MTA\ or by a guard (e.g.\ \NAME{TCP} \name{Wrappers}) before. The main advantage here is the minimal setup and maintainence work needed. This kind of access restriction is important to be implemented.
     5.8 +Several ways to restrict access are available. The most simple one is restriction by the \NAME{IP} address. No extra complexity is added this way, but the \NAME{IP} addresses have to be static or within known ranges. This approach is often used to allow relaying for local nets. The access check can be done by the \MTA\ or by a guard (e.g.\ \NAME{TCP} \name{Wrappers}) before. The main advantage here is the minimal setup and maintenance work needed. This kind of access restriction is important to be implemented.
     5.9  
    5.10 -This authentication based on \NAME{IP} addresses is impossible in situations where hosts with changing \NAME{IP} addresses, that are not part of a known subnet, need access. Then a authentication mechanism based on some \emph{secret} is required. Three common approaches exist:
    5.11 +This authentication based on \NAME{IP} addresses is impossible in situations where hosts with changing \NAME{IP} addresses, that are not part of a known sub net, need access. Then a authentication mechanism based on some \emph{secret} is required. Three common approaches exist:
    5.12  \begin{enumerate}
    5.13  	\item \SMTP-after-\NAME{POP}: Uses authentication on the \NAME{POP} protocol to permit incoming \SMTP\ connections for a limited time afterwards. The variant \SMTP-after-\NAME{IMAP} exists too.
    5.14  	\item \SMTP\ authentication: An extension to \SMTP. It allows to request authentication before mail is accepted. Here no helper protocols are needed.
    5.15 @@ -113,7 +113,7 @@
    5.16  
    5.17  The common way to encrypt \SMTP\ dialogs is using \name{Transport Layer Security} (short: \TLS, the successor of \NAME{SSL}). \TLS\ encrypts the datagrams of the \name{transport layer}. This means it works below the application protocols and can be used with any of them \citeweb{wikipedia:tls}.
    5.18  
    5.19 -Using secure tunnels that are provided by external programs, should be prefered over including encryption into the application, because the application needs not to bother with encryption then. Outgoing \SMTP\ connections can get encrypted using a secure tunnel, created by an external application (like \name{openssl}). But incoming connections can not use external secure tunnels, because the remote \NAME{IP} address is hidden then; all connections would appear to come from localhost instead. Figure \ref{fig:stunnel} depicts the situation of using an application like \name{stunnel} for incoming connections. The connection to port 25 comes from localhost and this information reaches the \MTA. Authentication based on \NAME{IP} addresses and many spam prevention methods are useless then.
    5.20 +Using secure tunnels that are provided by external programs, should be preferred over including encryption into the application, because the application needs not to bother with encryption then. Outgoing \SMTP\ connections can get encrypted using a secure tunnel, created by an external application (like \name{openssl}). But incoming connections can not use external secure tunnels, because the remote \NAME{IP} address is hidden then; all connections would appear to come from localhost instead. Figure \ref{fig:stunnel} depicts the situation of using an application like \name{stunnel} for incoming connections. The connection to port 25 comes from localhost and this information reaches the \MTA. Authentication based on \NAME{IP} addresses and many spam prevention methods are useless then.
    5.21  
    5.22  \begin{figure}
    5.23  	\begin{center}
    5.24 @@ -138,7 +138,7 @@
    5.25  
    5.26  Spam is identified by the results of a set of checks. Static rules, querying databases (\NAME{DNS} blacklists \cite{cole07} \cite{levine08}), requesting special client behavior (\name{greylisting} \cite{harris03}, \name{hashcash} \cite{back02}), or statistical analysis (\name{bayesian filters} \cite{graham02}) are checks that may be used. Running more checks leads to better results, but takes more system resources and more time.
    5.27  
    5.28 -Doing some basic checks during the \SMTP\ dialog seems to be a must \cite[page~25]{eisentraut05}. Including them into the \MTA\ makes them fast to avoid \SMTP\ dialog timeouts. For modularity and reusability reasons internal interfaces to specialized modules seem to be best.
    5.29 +Doing some basic checks during the \SMTP\ dialog seems to be a must \cite[page~25]{eisentraut05}. Including them into the \MTA\ makes them fast to avoid \SMTP\ dialog timeouts. For modularity and risibility reasons internal interfaces to specialized modules seem to be best.
    5.30  
    5.31  More detailed checks after the message is queued should be done using external scanners. Interfaces to invoke them need to be defined. (See also the remarks about \name{amavis} in the next section.)
    5.32  
    5.33 @@ -173,17 +173,17 @@
    5.34  
    5.35  
    5.36  \paragraph{\RG1: Security}
    5.37 -\MTA{}s are critical points for computer security, as they are accessible from external networks. They must be secured with high effort. Properties like the need for high privilege level, from outside influenced work load, work on unsafe data, and demand for reliability, increase the need for security. This is best done by modularization, also called \name{compartementalization}, as described in section \ref{sec:discussion-mta-arch}.
    5.38 +\MTA{}s are critical points for computer security, as they are accessible from external networks. They must be secured with high effort. Properties like the need for high privilege level, from outside influenced work load, work on unsafe data, and demand for reliability, increase the need for security. This is best done by modularization, also called \name{compartmentalization}, as described in section \ref{sec:discussion-mta-arch}.
    5.39  
    5.40  \masqmail\ needs to be secure enough for its target field of operation. \masqmail\ is targeted to workstations and private networks, with explicit warning to not use it on permanent online hosts \citeweb{masqmail:homepage2}. But as non-permanent online connections and trustable environments become rare, \masqmail's security should be so good, that it is usable with permanent online connections and in unsafe environments. For example should mails with bad content not break \masqmail.
    5.41  
    5.42  
    5.43  \paragraph{\RG2: Reliability}
    5.44 -Reliability is the second essential quality property for an \MTA. Mail for which the \MTA\ took responsibility must never get lost while it is within the \MTA{}s responsibility. The \MTA\ must not be \emph{the cause} of any mail loss, no matter what happens. Unreliable \mta{}s are of no value. However, as the mail transport infrastructure are distributed systems, one of the communication partners or the transport medium may crash at any time during mail tranfer. Thus reliability is needed for mail transfer communication too.
    5.45 +Reliability is the second essential quality property for an \MTA. Mail for which the \MTA\ took responsibility must never get lost while it is within the \MTA{}s responsibility. The \MTA\ must not be \emph{the cause} of any mail loss, no matter what happens. Unreliable \mta{}s are of no value. However, as the mail transport infrastructure are distributed systems, one of the communication partners or the transport medium may crash at any time during mail transfer. Thus reliability is needed for mail transfer communication too.
    5.46  
    5.47 -The goal is to transfer exactly one copy of the message. \person{Tanenbaum} evaluates the situation and comes to the conclusion that ``in general, there is no way to arrange this.'' \cite[pages~377--379]{tanenbaum02}. Only strategies where now mail gets lost are acceptable; he identifies three of them, but one generates more duplicates than the others, so two strategies remain. (1) The client always reissues the transfer; the server first sends an acknowledgement, then handles the transfer. (2) The client reissues the transfer only if no acknowledgement was received; the server first handles the transfer and sends the acknowledgement afterwards. The first strategy does not need acknowledgements at all, however, it will lose mail if the second transfer fails too.
    5.48 +The goal is to transfer exactly one copy of the message. \person{Tanenbaum} evaluates the situation and comes to the conclusion that ``in general, there is no way to arrange this.'' \cite[pages~377--379]{tanenbaum02}. Only strategies where now mail gets lost are acceptable; he identifies three of them, but one generates more duplicates than the others, so two strategies remain. (1) The client always reissues the transfer; the server first sends an acknowledgment, then handles the transfer. (2) The client reissues the transfer only if no acknowledgment was received; the server first handles the transfer and sends the acknowledgment afterwards. The first strategy does not need acknowledgments at all, however, it will lose mail if the second transfer fails too.
    5.49  
    5.50 -Hence, mail transfer between two processes must use the strategy: The client reissues if it receives no acknowledgement; the server first handles the message and then sends the acknowledgement. This strategy only leads to duplicates if a crash happens in the time between the message is fully transfered to the server and the acknowlegement is received by the client. No mail will get lost.
    5.51 +Hence, mail transfer between two processes must use the strategy: The client reissues if it receives no acknowledgment; the server first handles the message and then sends the acknowledgment. This strategy only leads to duplicates if a crash happens in the time between the message is fully transferred to the server and the acknowledgment is received by the client. No mail will get lost.
    5.52  
    5.53  
    5.54  \paragraph{\RG3: Robustness}
    5.55 @@ -286,7 +286,7 @@
    5.56  
    5.57  << smtp submission >> %fixme
    5.58  
    5.59 -\paragraph{\RF2: Queueing}
    5.60 +\paragraph{\RF2: Queuing}
    5.61  One single mail queue is used in \masqmail; it satisfies all current requirements.
    5.62  
    5.63  << persistence: DB >> %fixme
    5.64 @@ -307,10 +307,10 @@
    5.65  Similar is the situation for encryption which is also only available for outgoing channels; here a wrapper application like \name{openssl} is needed. This creates a secure tunnel to send mail trough, but state-of-the-art is using \NAME{STARTTLS}, which is not supported. For incoming channels, no encryption is available. The only possible setup to provide encryption of incoming channels is using an application like \name{stunnel} to translate between the secure connection to the remote host and the \MTA. Unfortunately, this suffers from the problem explained on page \pageref{fig:stunnel} in figure \ref{fig:stunnel}. Anyway, this would still be no \NAME{STARTTLS} support.
    5.66  
    5.67  \paragraph{\RF8: Spam handling}
    5.68 -\masqmail\ nowadays does not provide special support for spam filtering. Spam prevention by not accepting spam during the \SMTP\ dialog is not possible at all. Spam filtering is only possible by using two \masqmail\ instances with an external spam filter inbetween. The mail flow is from the receiving \MTA\ instance, which accepts mail, to the filter application that processes and possible modifies it, to the second \MTA\ which is responsible for further delivery of the mail. This is a concept that works in general. And it is a good concept in principle to separate work with clear interfaces. But the need of two instances of the same \MTA (each for only half of the job) with doubled setup, is more a work-around. Best is to have this data flow respected in the \MTA\ design, like in \postfix. But the more important part of spam handling, for sure, is done during the \SMTP\ dialog in completely refusing unwanted mail.
    5.69 +\masqmail\ nowadays does not provide special support for spam filtering. Spam prevention by not accepting spam during the \SMTP\ dialog is not possible at all. Spam filtering is only possible by using two \masqmail\ instances with an external spam filter in between. The mail flow is from the receiving \MTA\ instance, which accepts mail, to the filter application that processes and possible modifies it, to the second \MTA\ which is responsible for further delivery of the mail. This is a concept that works in general. And it is a good concept in principle to separate work with clear interfaces. But the need of two instances of the same \MTA (each for only half of the job) with doubled setup, is more a work-around. Best is to have this data flow respected in the \MTA\ design, like in \postfix. But the more important part of spam handling, for sure, is done during the \SMTP\ dialog in completely refusing unwanted mail.
    5.70  
    5.71  \paragraph{\RF9: Malware handling}
    5.72 -For malware handling applies nearly the same, except all checks are done after mail is accepted. So the possible setup is the same with the two \MTA\ instances and the filter inbetween. \masqmail\ does support such a setup, but not in a nice way.
    5.73 +For malware handling applies nearly the same, except all checks are done after mail is accepted. So the possible setup is the same with the two \MTA\ instances and the filter in between. \masqmail\ does support such a setup, but not in a nice way.
    5.74  
    5.75  \paragraph{\RF10: Archiving}
    5.76  There is currently no way of archiving every message going through \masqmail.
    5.77 @@ -321,7 +321,7 @@
    5.78  \masqmail's current security is bad. However, it seems acceptable for using \masqmail\ on workstations and private networks, if the environment is trustable and \masqmail\ is protected against remote attackers. In environments where untrusted components or persons have access to \masqmail, its security is too low.
    5.79  Its author states it ``is not designed to'' such usage \citeweb{masqmail:homepage2}. This 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. In any way, is a security report missing that confirms \masqmail's security level.
    5.80  
    5.81 -\masqmail\ uses conditional compilation to exclude unneeded functionality from the executable at complile time. Excluding code means excluding all bugs and weaknesses within this code too. Excluding unused code is a good concept to improve security.
    5.82 +\masqmail\ uses conditional compilation to exclude unneeded functionality from the executable at compile time. Excluding code means excluding all bugs and weaknesses within this code too. Excluding unused code is a good concept to improve security.
    5.83  
    5.84  \paragraph{\RG2: Reliability}
    5.85  Similar is its reliability not good enough. Situations where only one part of sent message was removed from the queue, and the other part remained as garbage, showed off \citeweb{debian:bug245882}. Problems with large mail and small bandwidth were also reported \citeweb{debian:bug216226}. Fortunately, lost email was no big problem yet, but \person{Kurth} warns:
    5.86 @@ -399,11 +399,11 @@
    5.87  
    5.88  
    5.89  \subsubsection*{\TODO4: Reliability (\RG2)}
    5.90 -Reliability is also to improve. It is a key quality property for an \MTA, and not good enough in \masqmail. Reliability is strong related to the queue, thus improvements there are favorable. Applying ideas of \name{crash-only software} \cite{candea03} will be a good step. \person{Candea} and \person{Fox} see in killing the process the best way to stop a running program. Doing so inevitably demands for good reliability of the queue, and the startup process inevitably demands for good recovery. The critical situations for reliability are nothing special anymore, they are common. Hence they are regulary tested and will definately work.
    5.91 +Reliability is also to improve. It is a key quality property for an \MTA, and not good enough in \masqmail. Reliability is strong related to the queue, thus improvements there are favorable. Applying ideas of \name{crash-only software} \cite{candea03} will be a good step. \person{Candea} and \person{Fox} see in killing the process the best way to stop a running program. Doing so inevitably demands for good reliability of the queue, and the start up process inevitably demands for good recovery. The critical situations for reliability are nothing special anymore, they are common. Hence they are regularly tested and will definitely work.
    5.92  
    5.93  
    5.94  \subsubsection*{\TODO5: Spam handling (\RF8)}
    5.95 -As authentication can be a guard against spam, filter facilities have lower priority. But basic spam filtering and interfaces for external tools should be implemented in future. Configuration guides for a setup using the approach of two \masqmail\ instances with a spam scanner inbetween should be written. And at least a basic kind of spam prevention during the \SMTP\ dialog should be implemented.
    5.96 +As authentication can be a guard against spam, filter facilities have lower priority. But basic spam filtering and interfaces for external tools should be implemented in future. Configuration guides for a setup using the approach of two \masqmail\ instances with a spam scanner in between should be written. And at least a basic kind of spam prevention during the \SMTP\ dialog should be implemented.
    5.97  
    5.98  
    5.99  \subsubsection*{\TODO6: Extendability (\RG4)}
   5.100 @@ -425,7 +425,7 @@
   5.101  
   5.102  \subsection{Possibilities}
   5.103  
   5.104 -Futher development of software can always go three different ways:
   5.105 +Further development of software can always go three different ways:
   5.106  \begin{enumerate}
   5.107  \item[S1:] Improve the current code base.
   5.108  \item[S2:] Add wrappers or interposition filters.
   5.109 @@ -435,7 +435,7 @@
   5.110  The first two strategies base on the available source code, and can be applied in combination. The third strategy splits from the old code base and starts over again. Wrappers and interposition filters would be outright included into a new architecture; they are a subset of a new design. Also parts of existing code can be used in a new design if appropriate.
   5.111  
   5.112  
   5.113 -The requirements are now regarded each on its own, and are linked to the development strategy that is prefered to reach each specific requirement. If some requirement is well achievable by using different strategies then it is linked to all of them. Implementing encryption (\TODO1) and authentication (\TODO2), for example, are limited to a narrow region in the code. Such features are addable to the current code base without much problem. In contrast can quality properties like reliability (\TODO4), extendability (\TODO6), and maintainability hardly be added to code afterwards---if at all. Security (\TODO3) is addable in a new design, of course, but also with wrappers or interposition filters.
   5.114 +The requirements are now regarded each on its own, and are linked to the development strategy that is preferred to reach each specific requirement. If some requirement is well achievable by using different strategies then it is linked to all of them. Implementing encryption (\TODO1) and authentication (\TODO2), for example, are limited to a narrow region in the code. Such features are addable to the current code base without much problem. In contrast can quality properties like reliability (\TODO4), extendability (\TODO6), and maintainability hardly be added to code afterwards---if at all. Security (\TODO3) is addable in a new design, of course, but also with wrappers or interposition filters.
   5.115  
   5.116  This linking of strategies to the requirements is shown in table \ref{tab:strategies}. The requirements are ordered by their focus.
   5.117  
   5.118 @@ -448,7 +448,7 @@
   5.119  \end{table}
   5.120  
   5.121  
   5.122 -Next, the best strategy for further development needs to be discovered. Therefore a score for each strategy is obtained now by summing up the focus points of each requirement for which a strategy is prefered. Herefore only positive focus points are regarded, with each plus symbol counting one. Requirements with negative focus are not regareded because they are already or nearly reached, but the view here is on outstanding work. %(Respecting negative focus points leads to a similar result.)
   5.123 +Next, the best strategy for further development needs to be discovered. Therefore a score for each strategy is obtained now by summing up the focus points of each requirement for which a strategy is preferred. Therefore only positive focus points are regarded, with each plus symbol counting one. Requirements with negative focus are not regarded because they are already or nearly reached, but the view here is on outstanding work. %(Respecting negative focus points leads to a similar result.)
   5.124  
   5.125  Strategy 1 (Improve current code) has a score of 9 points. Strategy 2 (Wrappers and interposition filters) has a score of 7 points. Strategy 3 (A new design) scores on top with 17 points. \St1 and \St2 can be used in combination; the combined score is 13 points. Thus strategy 3 ranges first, followed by the combination of strategy 1 and 2.
   5.126  
   5.127 @@ -466,7 +466,7 @@
   5.128  
   5.129  \subsubsection*{Quality improvements}
   5.130  
   5.131 -Most quality properties can hardly be added to a software afterwards. Hence, if reliability, extendability, or maintainability shall be improved, a redesign of \masqmail\ is the best way to take. The wish to improve quality inevitably point towards a modular architecture. Modularity with internal and external interfaces is highly prefered from the architectural point of view (see section \ref{sec:discussion-mta-arch}). The need for further features, especially ones that require changes in \masqmail's structure, support the decision for a new design too. Hence a rewrite is enfavored if \masqmail\ should become a modern \MTA, with good quality properties.
   5.132 +Most quality properties can hardly be added to a software afterwards. Hence, if reliability, extendability, or maintainability shall be improved, a redesign of \masqmail\ is the best way to take. The wish to improve quality inevitably point towards a modular architecture. Modularity with internal and external interfaces is highly preferred from the architectural point of view (see section \ref{sec:discussion-mta-arch}). The need for further features, especially ones that require changes in \masqmail's structure, support the decision for a new design too. Hence a rewrite is favored if \masqmail\ should become a modern \MTA, with good quality properties.
   5.133  
   5.134  
   5.135  
   5.136 @@ -482,7 +482,7 @@
   5.137  
   5.138  They also suggest to add wrappers and interposition filters \emph{around} applications, but more as repair techniques if it is not possible to design security \emph{into} a software the first way \cite[pages~71--72]{graff03}.
   5.139  
   5.140 -\person{Hafiz} adds: ``The major idea is that security cannot be retrofitted \emph{into} an architecture.'' \cite[page 64]{hafiz05} (emphasisis added).
   5.141 +\person{Hafiz} adds: ``The major idea is that security cannot be retrofitted \emph{into} an architecture.'' \cite[page 64]{hafiz05} (emphasis added).
   5.142  
   5.143  
   5.144  
   5.145 @@ -504,7 +504,7 @@
   5.146  
   5.147  \subsubsection*{Risks}
   5.148  
   5.149 -The gained result might still overwights the development effort. But risks are something more to consider.
   5.150 +The gained result might still outweighs the development effort. But risks are something more to consider.
   5.151  
   5.152  A redesign and rewrite of software from scratch is hard. It takes time to design a new architecture, which then must prove that it is as good as expected. As well is much time and work needed to implement the design, test it, fix bugs, and so on. If flaws in the design appear during prototype implementation, it is necessary to start again.
   5.153  
   5.154 @@ -547,11 +547,11 @@
   5.155  
   5.156  A new design does protect against such dead ends.
   5.157  
   5.158 -Changing requirements are one possible dead end if the software does not evolve with them. A famous example is \sendmail, which had an almost monopoly for a long time. But when security became important \sendmail\ was only repaired instead of removing the problem sources---its unsecure design. Thus security problems reappeared and over the years \sendmail's market share shrinked as more secure \MTA{}s became available. %fixme: declined ??
   5.159 +Changing requirements are one possible dead end if the software does not evolve with them. A famous example is \sendmail, which had an almost monopoly for a long time. But when security became important \sendmail\ was only repaired instead of removing the problem sources---its insecure design. Thus security problems reappeared and over the years \sendmail's market share shrank as more secure \MTA{}s became available. %fixme: declined ??
   5.160  \sendmail's reaction to the new requirements, in form of \name{sendmail X} and \name{MeTA1}, came much to late---the users already switched to other \MTA{}s. Redesigning a software as requirements change helps keeping it alive. % add quote: ``one thing surely remains: change'' (something like that)
   5.161  
   5.162  Another danger is the dead end of complexity which is likely to appear by constantly working on the same code base. It is even more likely if the code base has a monolithic architecture. A good example for simplicity is \qmail\ which consists of small independent modules, each with only about one thousand lines of code. %fixme: proof
   5.163 -Such simple code makes it obvious to understand what it does. The \name{suckless} project \citeweb{suckless.org} for example advertizes such a philosophy of small and simple software by following the thoughts of the \unix\ inventors \cite{kernighan84} \cite{kernighan99}. Simple, small, and clear code avoids complexity and is thus also a strong prequisite for security.
   5.164 +Such simple code makes it obvious to understand what it does. The \name{suckless} project \citeweb{suckless.org} for example advertises such a philosophy of small and simple software by following the thoughts of the \unix\ inventors \cite{kernighan84} \cite{kernighan99}. Simple, small, and clear code avoids complexity and is thus also a strong prerequisite for security.
   5.165  
   5.166  
   5.167  
   5.168 @@ -559,7 +559,7 @@
   5.169  
   5.170  \subsubsection*{Modularity}
   5.171  
   5.172 -The avoidence of dead ends is essential for further development on current code too. Hence it is mandatory to refactor the existing code base sooner or later. Most important is the intention to modularize it, as it improves many quality requirements, eases further development, and essentially improves securtiy.
   5.173 +The avoidance of dead ends is essential for further development on current code too. Hence it is mandatory to refactor the existing code base sooner or later. Most important is the intention to modularize it, as it improves many quality requirements, eases further development, and essentially improves security.
   5.174  
   5.175  One example how modular structure makes it easy to add further functionality: \person{Sill} describes that integrating the \name{amavis} filter framework into the \qmail\ system can be done by renaming the \name{qmail-queue} module to \name{qmail-queue-real} and renaming the \name{amavis} to \name{qmail-queue} \cite[section~12.7.1]{sill02}. Nothing more in the \qmail\ system needs to be changed. This is a very admirable approach, but only possible in a modular system that consists of independent executables.
   5.176  
   5.177 @@ -588,7 +588,7 @@
   5.178  
   5.179  It is important to keep the time dimension in mind. This includes the  separation into a short-time and a long-time view. The short-time view shall cover between two and four years. The long-time view is the following time. % fixme: find sources!
   5.180  
   5.181 -In the short-time view, the effort for improving the existing code is much smaller than the effort for a new design plus improvements. But to have similar quality properties at the end of the short-time frame, a \masqmail\ that is based on current code will probably require nearly as much effort as a new designed \masqmail\ will take. For all further development afterwards, the new design will scale well while the old code will require exponentiel more work.
   5.182 +In the short-time view, the effort for improving the existing code is much smaller than the effort for a new design plus improvements. But to have similar quality properties at the end of the short-time frame, a \masqmail\ that is based on current code will probably require nearly as much effort as a new designed \masqmail\ will take. For all further development afterwards, the new design will scale well while the old code will require exponential more work.
   5.183  
   5.184  In the long-time view, a restructuring for modularity is necessary anyway. The question is, when to do it: Right at the start in a new design, or later in some restructuring.
   5.185  
   5.186 @@ -598,7 +598,7 @@
   5.187  
   5.188  \subsubsection*{The problem with ``good enough''}
   5.189  
   5.190 -The decision for later restructuring is problematic. Functionality is often more wanted than quality, so further function is prefered over better quality, as quality is still ``good enough''. But it might be still ``good enough'' the next time, and the time after that one, and so on.
   5.191 +The decision for later restructuring is problematic. Functionality is often more wanted than quality, so further function is preferred over better quality, as quality is still ``good enough''. But it might be still ``good enough'' the next time, and the time after that one, and so on.
   5.192  
   5.193  Quality improving is no popular work but it is required to avoid dead ends. As more code increases the work that needs to be done for quality and modularity improvements, it is better to do these improvements early. Afterwards all further development profits from it.
   5.194  
   5.195 @@ -618,7 +618,7 @@
   5.196  
   5.197  Good concepts, sound design, and a sane philosophy gives users good feelings for the software and faith in it. They become interested in using it and to contribute. In contrast does constantly repairing and reappearing weaknesses leave a bad feeling.
   5.198  
   5.199 -The motivation most volunteer developers have is their wish of doing good work to create software of value. Projects that follow admireable plans towards a good product will motivate volunteers to help with it. More helpers can get the 2,5 man-years for a new design in less absolute time done. Additionally is a good developers base the best start for a good user base, and users define a software's value.
   5.200 +The motivation most volunteer developers have is their wish of doing good work to create software of value. Projects that follow admire able plans towards a good product will motivate volunteers to help with it. More helpers can get the 2,5 man-years for a new design in less absolute time done. Additionally is a good developers base the best start for a good user base, and users define a software's value.
   5.201  
   5.202  
   5.203  
   5.204 @@ -629,9 +629,9 @@
   5.205  
   5.206  \section{Result}
   5.207  
   5.208 -This chapter identified the requirements and the outstanding work to achieve them. Their importance and the required work on them lead to a focus ranking amoung the requirements, which resulted in a list of tasks to do. Afterwards possible development strategies to control the work process were compared and discussed.
   5.209 +This chapter identified the requirements and the outstanding work to achieve them. Their importance and the required work on them lead to a focus ranking among the requirements, which resulted in a list of tasks to do. Afterwards possible development strategies to control the work process were compared and discussed.
   5.210  
   5.211 -Strategy 3 (A new design) is slightly prefered over the combination of strategy 1 (Improve existing code) and 2 (Add wrappers and interposition filters) in regard of the requirements.
   5.212 +Strategy 3 (A new design) is slightly preferred over the combination of strategy 1 (Improve existing code) and 2 (Add wrappers and interposition filters) in regard of the requirements.
   5.213  
   5.214  The discussion afterwards did generally support the new design strategy. But some arguments stand against it. These are:
   5.215  
   5.216 @@ -643,10 +643,10 @@
   5.217  
   5.218  The first two arguments are only relevant for the short-time view, because both will become \emph{support arguments} for the new design, once the Break Even point is reached.
   5.219  
   5.220 -The third argument, the risks, remain. There are risk in every investion. Taking no risks means remaining the same, means drifting towards a dead end in a world that does change.
   5.221 +The third argument, the risks, remain. There are risk in every investment. Taking no risks means remaining the same, means drifting towards a dead end in a world that does change.
   5.222  
   5.223  
   5.224 -With respect to the current situation, the suggested further development plan for \masqmail\ is splitted into a short-time plan and a long-time plan:
   5.225 +With respect to the current situation, the suggested further development plan for \masqmail\ is split into a short-time plan and a long-time plan:
   5.226  
   5.227  \begin{enumerate}
   5.228  \item The short-time plan: Add the most needed features, being encryption, authentication, and security wrappers, to the current code base.
   5.229 @@ -656,7 +656,7 @@
   5.230  The background thought is to first do the most needed stuff on the existing code to keep %fixme: erhalten
   5.231  it usable. This satisfies the urgent needs and removes the time pressure from the development of the new design. After this is done, a new designed \masqmail\ should be developed from scratch. This is the work for the future. It shall, after it is usable and throughout tested, supersede the old \masqmail.
   5.232  
   5.233 -The basic idea is, regularly developing a new design from scratch while the current version is still in use and gets repaired. Hence a modern design will inherit an old one in regular intervals. This is a very future-proove concept that combines the best of both worlds. The price to pay is only the increased work which gets covered %fixme: uebernommen
   5.234 +The basic idea is, regularly developing a new design from scratch while the current version is still in use and gets repaired. Hence a modern design will inherit an old one in regular intervals. This is a very future-proof concept that combines the best of both worlds. The price to pay is only the increased work which gets covered %fixme: uebernommen
   5.235  by volunteers that \emph{want} to do it.
   5.236  
   5.237