1.1 --- a/thesis/tex/5-Improvements.tex	Fri Jan 16 09:46:05 2009 +0100
     1.2 +++ b/thesis/tex/5-Improvements.tex	Fri Jan 16 10:35:48 2009 +0100
     1.3 @@ -9,7 +9,7 @@
     1.4  
     1.5  
     1.6  
     1.7 -\section{On base of current code}
     1.8 +\section{Based on current code}
     1.9  
    1.10  The first three \TODO{}s are implementable by improving the current code or by adding wrappers or interposition filters. The following sections describe solution approaches to do that work.
    1.11  
    1.12 @@ -65,7 +65,7 @@
    1.13  
    1.14  \begin{enumerate}
    1.15  	\item \SMTP-after-\NAME{POP}: uses authenication on the \NAME{POP} protocol to permit incoming \SMTP\ connections for a limited time afterwards.
    1.16 -	\item \SMTP authentication: is an extension to \SMTP. Authentication can be requested before mail is accepted.
    1.17 +	\item \SMTP\ authentication: is an extension to \SMTP. Authentication can be requested before mail is accepted.
    1.18  	\item Certificates: confirm the identity of someone.
    1.19  \end{enumerate}
    1.20  
    1.21 @@ -212,14 +212,15 @@
    1.22  	\item a list of users (e.g.\ ``\texttt{bob: alice, john@example.com}'')
    1.23  	\item a command (e.g.\ ``\texttt{bob: |foo}'')
    1.24  \end{enumerate}
    1.25 -Addresses expanding to lists of users lead to more envelopes. Aliases changing the reciptients domain part may require a different route to use.
    1.26 +Addresses expanding to lists of users lead to more envelopes. Aliases changing the reciptients domain part may make the message unsuitable for a specific online route.
    1.27  
    1.28  Aliasing is often handled in expanding the alias and reinjecting the mail into the system. Unfortunately, the mail is processed twice then; additionally does the system have to handle more mail this way. If it is wanted to check the new recipient address for acceptance and do all processing again, then reinjecting it is the best choice.
    1.29  
    1.30  
    1.31  
    1.32 -\subsubsection*{Choose route to use}
    1.33 +\subsubsection*{Route management}
    1.34  
    1.35 +%fixme: rework!!
    1.36  One key feature of \masqmail\ is its ability to send mail out in different ways. The decision is based on the current online state and whether a route may be used for a message or not. The online state can be retrieved in tree ways, explained in \ref{sec:fixme}. A route to send is found by checking every available route for being able to transfer the current message, until one matches.
    1.37  
    1.38  This functionality should be implemented in the module that is responsible to invoke one of the outgoing channel modules (for example the one for \SMTP\ or the pipe module).
    1.39 @@ -265,16 +266,21 @@
    1.40  \subsubsection*{Spam prevention}
    1.41  
    1.42  ---
    1.43 -Spam is a major threat nowadays and the goal is to reduce it to a bearable level (see section \ref{sec:swot-analysis}). Spam fighting is a war are where the good guys tend to lose. Putting too much effort there will result in few gain. Real success will only be possible with new---better---protocols and abandonning the weak legacy technologies. Hence \masqmail\ should be able to provide state-of-the-art spam protection, but not more.
    1.44 +
    1.45 +Spam is a major threat nowadays and the goal is to reduce it to a bearable level (see section \ref{sec:swot-analysis}). Spam fighting is a war in which the good guys tend to lose. Putting too much effort there will result in few gain. Real success will only be possible with new---better---protocols and abandonning the weak legacy technologies. Hence \masqmail\ should be able to provide state-of-the-art spam protection, but not more.
    1.46 +
    1.47  ---
    1.48  
    1.49  Spam is a major threat to email, as described in section \ref{sec:swot-analysis}. The two main problems are forgable sender addresses and that it is cheap to send hundreds of thousands of messages. Hence, spam senders can operate in disguise and have minimal cost.
    1.50  
    1.51 -As spam is not just a nuisance for end users, but also for the infrastructure---the \mta{}s---by increasing the amount of mail messages, \MTA{}s need to protect themself. Two approaches are used.
    1.52 +As spam is not just a nuisance for end users but also for the infrastructure---the \mta{}s---by increasing the amount of mail messages. Thus \MTA{}s need to protect themself. Two different approaches are used:
    1.53  
    1.54 -First refusing spam during the \SMTP\ dialog. This is the way it was meant by the designers of the \SMTP\ protocol. They thought checking the sender and reciptient mail addresses would be enough, but as they are forgable it is not. More and more complex checks need to be done. Checking needs time, but \SMTP\ dialogs time out if it takes too long. Thus only limited time can be used, during the \SMTP\ dialog, for checking if a message seems to be spam. The advantage is that acceptance of bad messages can be simply refused---no responsibility for the message is takes and no further system load is added. See \RFC2505 (especially section 1.5) for detail.
    1.55 +\begin{enumerate}
    1.56 +\item Refusing spam during the \SMTP\ dialog. This is the way it was meant by the designers of the \SMTP\ protocol. They thought checking the sender and reciptient mail addresses would be enough, but as they are forgable it is not. More and more complex checks need to be done. Checking needs time, but \SMTP\ dialogs time out if it takes too long. Thus only limited time can be used, during the \SMTP\ dialog, for checking if a message seems to be spam. The advantage is that acceptance of bad messages can be simply refused---no responsibility for the message is taken and no further system load is added. See \RFC2505 (especially section 1.5) for detail.
    1.57  
    1.58 -Second checking for spam after the mail was accepted and queued. Here more processing time can be invested, so more detailed checks can be done. But, as responsibility for messages was taken by accepting them, it is no choice to simply delete spam mail. Checks for spam do not lead to sure results, they just indicate the possibility the message is unwanted mail. \person{Eisentraut} indicates actions to take after a message is recognized as probably spam \cite[pages 18--20]{eisentraut05}. The only acceptable one, for mail the \MTA\ is responsible for, is adding further or rewriting existent header lines. Thus all further work on the message is the same as for non-spam messages.
    1.59 +\item
    1.60 +Checking for spam after the mail was accepted and queued. Here more processing time can be invested, so more detailed checks can be done. But, as responsibility for messages was taken by accepting them, it is no choice to simply delete spam mail. Checks for spam do not lead to sure results, they just indicate the possibility the message is unwanted mail. \person{Eisentraut} indicates actions to take after a message is recognized as probably spam \cite[pages 18--20]{eisentraut05}. The only acceptable one, for mail the \MTA\ is responsible for, is adding further or rewriting existent header lines. Thus all further work on the message is the same as for non-spam messages.
    1.61 +\end{enumerate}
    1.62  
    1.63  Modern \MTA{}s use both techniques in combination. Checks during the \SMTP\ dialog tend to be implemented in the \mta\ to make it fast; checks after the message was queued are often done using external programs (\name{spamassassin} is a well known one). \person{Eisentraut} sees the checks during the \SMTP\ dialog to be essentiell: ``Ganz ohne Analyse während der SMTP-Phase kommt sowieso kein MTA aus, und es ist eine Frage der Einschätzung, wie weit man diese Phase belasten möchte.''\cite[page 25]{eisentraut05} (translated: ``No \MTA\ can go without analysis during the \SMTP\ dialog, anyway, and it is a question of estimation how much to stress this period.'')
    1.64  
    1.65 @@ -375,6 +381,7 @@
    1.66  
    1.67  
    1.68  The \name{queue-out} module takes messages from the \name{outgoing} queue, queries information about the online connection, and then selects matching routes, creates envelopes for each recipient and passes the messages to the correct transport module. Successfully transfered messages are removed from the \name{outgoing} queue. This module includes some tasks specific to \masqmail.
    1.69 +%fixme: rework route selection
    1.70  
    1.71  
    1.72  The \name{incoming} queue stores messages received via one of the incoming channels. The messages are in unprocessed form; only envelope data is prepended.