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author meillo@marmaro.de
date Tue, 03 Feb 2009 18:01:33 +0100
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17 \subsubsection{Mail agents} 17 \subsubsection{Mail agents}
18 \index{mail agents} 18 \index{mail agents}
19 19
20 This thesis will frequently use the three terms: \MTA, \MUA{}, and \MDA{}, naming the three different kinds of 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 when passing through the system. 20 This thesis will frequently use the three terms: \MTA, \MUA{}, and \MDA{}, naming the three different kinds of 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 when passing through the system.
21 21
22 \begin{description} 22 \begin{description}
23 \item[\MTA:] 23 \item[\MTA:]
24 \index{mta} 24 \index{mta}
25 \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}. 25 \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}.
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27 \item[\MUA{}:] 27 \item[\MUA{}:]
28 \index{mua} 28 \index{mua}
29 \name{Mail User Agents} are the software users deal with. A user writes and reads email with it. The \MUA{} passes outgoing mail to the nearest \MTA. Also the \MUA{} displays the contents of the user's mailbox. Well known \MUA{}s are \name{Mozilla Thunderbird} and \name{mutt} on \unix\ systems, and \name{Microsoft Outlook} on \name{Windows}. 29 \name{Mail User Agents} are the software users deal with. A user writes and reads email with it. The \MUA{} passes outgoing mail to the nearest \MTA. Also the \MUA{} displays the contents of the user's mailbox. Well known \MUA{}s are \name{Mozilla Thunderbird} and \name{mutt} on \unix\ systems, and \name{Microsoft Outlook} on \name{Windows}.
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118 \hfill\citeweb{packages.debian:masqmail} 118 \hfill\citeweb{packages.debian:masqmail}
119 \end{quote} 119 \end{quote}
120 120
121 The program is a good replacement ``in these cases'' but not generally, since it lacks essential features for running on publically accessable mail servers. It is primarily not secure enough for being accessible from untrusted locations. 121 The program is a good replacement ``in these cases'' but not generally, since it lacks essential features for running on publically accessable mail servers. It is primarily not secure enough for being accessible from untrusted locations.
122 122
123 \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 online connection. These features are explained in more detail in section \ref{sec:masqmail-features}. 123 \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 online connection. These features are explained in more detail in section~\ref{sec:masqmail-features}.
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125 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 \MTA{}s. 125 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 \MTA{}s.
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127 \masqmail\ is designed to run on workstations and on servers in small networks, like they are common in \NAME{SOHO}s (\name{Small Offices/Home Offices}). 127 \masqmail\ is designed to run on workstations and on servers in small networks, like they are common in \NAME{SOHO}s (\name{Small Offices/Home Offices}).
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130 130
131 \subsubsection*{Typical usage scenarios} 131 \subsubsection*{Typical usage scenarios}
132 132
133 This section describes three common setups that make sensible use of \masqmail. The first two are shown in figure \ref{fig:masqmail-typical-usage}. 133 This section describes three common setups that make sensible use of \masqmail. The first two are shown in figure~\ref{fig:masqmail-typical-usage}.
134 134
135 \begin{figure} 135 \begin{figure}
136 \begin{center} 136 \begin{center}
137 \includegraphics[scale=0.75]{img/masqmail-typical-usage.eps} 137 \includegraphics[scale=0.75]{img/masqmail-typical-usage.eps}
138 \end{center} 138 \end{center}
148 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; only host names would differ. 148 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; only host names would differ.
149 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. 149 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.
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151 \item[Scenario 2:] 151 \item[Scenario 2:]
152 \label{scenario2} 152 \label{scenario2}
153 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, this can be solved by mounting the user's mailbox from the server to the workstation or by using \NAME{POP3} or \NAME{IMAP}. Mail transfer from the \NAME{ISP} to the local server needs \NAME{POP3} or \NAME{IMAP} as well. 153 In the same network but with a server, one could have \masqmail\ running on the server and using simple forwarders (see section~\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, this can be solved by mounting the user's mailbox from the server to the workstation or by using \NAME{POP3} or \NAME{IMAP}. Mail transfer from the \NAME{ISP} to the local server needs \NAME{POP3} or \NAME{IMAP} as well.
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155 \item[Scenario 3:] 155 \item[Scenario 3:]
156 \label{scenario3} 156 \label{scenario3}
157 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 becomes more and more common. Different networks demand for 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. 157 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 becomes more and more common. Different networks demand for 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.
158 \end{description} 158 \end{description}
222 \item Direct delivery to local mailboxes (in \name{mbox} or \name{maildir} format) 222 \item Direct delivery to local mailboxes (in \name{mbox} or \name{maildir} format)
223 \item Local pipes to pass mail to a program (e.g.\ to \MDA{}s or to gateways to \NAME{UUCP} or fax) 223 \item Local pipes to pass mail to a program (e.g.\ to \MDA{}s or to gateways to \NAME{UUCP} or fax)
224 \item \NAME{TCP} sockets to transfer mail to other \MTA{}s using the \SMTP\ protocol 224 \item \NAME{TCP} sockets to transfer mail to other \MTA{}s using the \SMTP\ protocol
225 \end{enumerate} 225 \end{enumerate}
226 226
227 Figure \ref{fig:masqmail-channels} shows this as a picture. (The ``online state'' input is explained a bit later.) 227 Figure~\ref{fig:masqmail-channels} shows this as a picture. (The ``online state'' input is explained a bit later.)
228 228
229 \begin{figure} 229 \begin{figure}
230 \begin{center} 230 \begin{center}
231 \includegraphics[scale=0.75]{img/masqmail-channels.eps} 231 \includegraphics[scale=0.75]{img/masqmail-channels.eps}
232 \end{center} 232 \end{center}
295 I'm sure you can make any \MTA\ behave nicely when offline, but it was a chore 295 I'm sure you can make any \MTA\ behave nicely when offline, but it was a chore
296 with all of them. 296 with all of them.
297 \hfill\citeweb[post~\#8]{ubuntuforums:simple-mailer} 297 \hfill\citeweb[post~\#8]{ubuntuforums:simple-mailer}
298 \end{quote} 298 \end{quote}
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300 Not to forget \masqmail's size. \masqmail\ is much smaller than full-blown \MTA{}s like \sendmail, \postfix, or \exim, and still smaller than \qmail. (See section \ref{sec:mta-comparison} for details.) This makes \masqmail\ a good choice for workstations or even embedded computers. 300 Not to forget \masqmail's size. \masqmail\ is much smaller than full-blown \MTA{}s like \sendmail, \postfix, or \exim, and still smaller than \qmail. (See section~\ref{sec:mta-comparison} for details.) This makes \masqmail\ a good choice for workstations or even embedded computers.
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302 Again words of a user who chose \masqmail\ as \MTA\ on his old laptop with a 75 megahertz processor and eight megabytes of \NAME{RAM}: 302 Again words of a user who chose \masqmail\ as \MTA\ on his old laptop with a 75 megahertz processor and eight megabytes of \NAME{RAM}:
303 \begin{quote} 303 \begin{quote}
304 Masqmail appears to be a great sendmail replacement in this case. It's small and is built to support sending mail ``off-line'', and to connecting to the \SMTP\ servers of several \NAME{ISP}s. 304 Masqmail appears to be a great sendmail replacement in this case. It's small and is built to support sending mail ``off-line'', and to connecting to the \SMTP\ servers of several \NAME{ISP}s.
305 \hfill\citeweb{stosberg:low-mem-laptop} 305 \hfill\citeweb{stosberg:low-mem-laptop}