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<a class="previous_page" href="filter_ch02.html"><-previous</a><a class="next_page" href="filter_ch04.html">next-></a><div id="chapter" class="chapter">
<h2 id="CHAPeximfilter" class="">Chapter 3 - Exim filter files</h2>
<p>
This chapter contains a full description of the contents of Exim filter files.
</p>
<div class="section">
<h3 id="SEC17" class="">1. Format of Exim filter files</h3>
<p>
Apart from leading white space, the first text in an Exim filter file must be
</p>
<div class="docbook_literallayout"><pre>
# Exim filter
</pre></div>
<p>
This is what distinguishes it from a conventional <span class="docbook_filename">.forward</span> file or a Sieve
filter file. If the file does not have this initial line (or the equivalent for
a Sieve filter), it is treated as a conventional <span class="docbook_filename">.forward</span> file, both when
delivering mail and when using the <span class="docbook_option">-bf</span> testing mechanism. The white space
in the line is optional, and any capitalization may be used. Further text on
the same line is treated as a comment. For example, you could have
</p>
<div class="docbook_literallayout"><pre>
# Exim filter <<== do not edit or remove this line!
</pre></div>
<p>
The remainder of the file is a sequence of filtering commands, which consist of
keywords and data values. For example, in the command
</p>
<div class="docbook_literallayout"><pre>
deliver gulliver@lilliput.fict.example
</pre></div>
<p>
the keyword is <code class="docbook_literal">deliver</code> and the data value is
<code class="docbook_literal">gulliver@lilliput.fict.example</code>. White space or line breaks separate the
components of a command, except in the case of conditions for the <span class="docbook_command">if</span>
command, where round brackets (parentheses) also act as separators. Complete
commands are separated from each other by white space or line breaks; there are
no special terminators. Thus, several commands may appear on one line, or one
command may be spread over a number of lines.
</p>
<p>
If the character # follows a separator anywhere in a command, everything from
# up to the next newline is ignored. This provides a way of including comments
in a filter file.
</p>
</div>
<div class="section">
<h3 id="SEC18" class="">2. Data values in filter commands</h3>
<p>
There are two ways in which a data value can be input:
</p>
<ul>
<li>
<p>
If the text contains no white space, it can be typed verbatim. However, if it
is part of a condition, it must also be free of round brackets (parentheses),
as these are used for grouping in conditions.
</p>
</li>
<li>
<p>
Otherwise, text must be enclosed in double quotation marks. In this case, the
character \ (backslash) is treated as an “escape character” within the
string, causing the following character or characters to be treated specially:
</p>
<div class="docbook_literallayout"><pre>
<code class="docbook_literal">\n</code> is replaced by a newline
<code class="docbook_literal">\r</code> is replaced by a carriage return
<code class="docbook_literal">\t</code> is replaced by a tab
</pre></div>
</li>
</ul>
<p>
Backslash followed by up to three octal digits is replaced by the character
specified by those digits, and <code class="docbook_literal">\x</code> followed by up to two hexadecimal digits
is treated similarly. Backslash followed by any other character is replaced by
the second character, so that in particular, <code class="docbook_literal">\"</code> becomes <code class="docbook_literal">"</code> and <code class="docbook_literal">\\</code>
becomes <code class="docbook_literal">\</code>. A data item enclosed in double quotes can be continued onto the
next line by ending the first line with a backslash. Any leading white space at
the start of the continuation line is ignored.
</p>
<p>
In addition to the escape character processing that occurs when strings are
enclosed in quotes, most data values are also subject to <span class="docbook_emphasis">string expansion</span>
(as described in the next section), in which case the characters <code class="docbook_literal">$</code> and
<code class="docbook_literal">\</code> are also significant. This means that if a single backslash is actually
required in such a string, and the string is also quoted, <code class="docbook_literal">\\\\</code> has to be
entered.
</p>
<p>
The maximum permitted length of a data string, before expansion, is 1024
characters.
</p>
</div>
<div class="section">
<h3 id="SECTfilterstringexpansion" class="">3. String expansion</h3>
<p>
Most data values are expanded before use. Expansion consists of replacing
substrings beginning with <code class="docbook_literal">$</code> with other text. The full expansion facilities
available in Exim are extensive. If you want to know everything that Exim can
do with strings, you should consult the chapter on string expansion in the Exim
documentation.
</p>
<p>
In filter files, by far the most common use of string expansion is the
substitution of the contents of a variable. For example, the substring
</p>
<div class="docbook_literallayout"><pre>
$reply_address
</pre></div>
<p>
is replaced by the address to which replies to the message should be sent. If
such a variable name is followed by a letter or digit or underscore, it must be
enclosed in curly brackets (braces), for example,
</p>
<div class="docbook_literallayout"><pre>
${reply_address}
</pre></div>
<p>
If a <code class="docbook_literal">$</code> character is actually required in an expanded string, it must be
escaped with a backslash, and because backslash is also an escape character in
quoted input strings, it must be doubled in that case. The following two
examples illustrate two different ways of testing for a <code class="docbook_literal">$</code> character in a
message:
</p>
<div class="docbook_literallayout"><pre>
if $message_body contains \$ then ...
if $message_body contains "\\$" then ...
</pre></div>
<p>
You can prevent part of a string from being expanded by enclosing it between
two occurrences of <code class="docbook_literal">\N</code>. For example,
</p>
<div class="docbook_literallayout"><pre>
if $message_body contains \N$$$$\N then ...
</pre></div>
<p>
tests for a run of four dollar characters.
</p>
</div>
<div class="section">
<h3 id="SEC19" class="">4. Some useful general variables</h3>
<p>
A complete list of the available variables is given in the Exim documentation.
This shortened list contains the ones that are most likely to be useful in
personal filter files:
</p>
<p>
$body_linecount: The number of lines in the body of the message.
</p>
<p>
$body_zerocount: The number of binary zero characters in the body of the
message.
</p>
<p>
$home: In conventional configurations, this variable normally contains the
user’s home directory. The system administrator can, however, change this.
</p>
<p>
$local_part: The part of the email address that precedes the @ sign –
normally the user’s login name. If support for multiple personal mailboxes is
enabled (see section <a href="filter_ch03.html#SECTmbox" title="3. Exim filter files">3.31</a> below) and a prefix or suffix for the local
part was recognized, it is removed from the string in this variable.
</p>
<p>
$local_part_prefix: If support for multiple personal mailboxes is enabled
(see section <a href="filter_ch03.html#SECTmbox" title="3. Exim filter files">3.31</a> below), and a local part prefix was recognized,
this variable contains the prefix. Otherwise it contains an empty string.
</p>
<p>
$local_part_suffix: If support for multiple personal mailboxes is enabled
(see section <a href="filter_ch03.html#SECTmbox" title="3. Exim filter files">3.31</a> below), and a local part suffix was recognized,
this variable contains the suffix. Otherwise it contains an empty string.
</p>
<p>
$message_body: The initial portion of the body of the message. By default,
up to 500 characters are read into this variable, but the system administrator
can configure this to some other value. Newlines in the body are converted into
single spaces.
</p>
<p>
$message_body_end: The final portion of the body of the message, formatted
and limited in the same way as $message_body.
</p>
<p>
$message_body_size: The size of the body of the message, in bytes.
</p>
<p>
$message_exim_id: The message’s local identification string, which is unique
for each message handled by a single host.
</p>
<p>
$message_headers: The header lines of the message, concatenated into a
single string, with newline characters between them.
</p>
<p>
$message_size: The size of the entire message, in bytes.
</p>
<p>
$original_local_part: When an address that arrived with the message is
being processed, this contains the same value as the variable $local_part.
However, if an address generated by an alias, forward, or filter file is being
processed, this variable contains the local part of the original address.
</p>
<p>
$reply_address: The contents of the <span class="docbook_emphasis">Reply-to:</span> header, if the message
has one; otherwise the contents of the <span class="docbook_emphasis">From:</span> header. It is the address to
which normal replies to the message should be sent.
</p>
<p>
$return_path: The return path – that is, the sender field that will be
transmitted as part of the message’s envelope if the message is sent to another
host. This is the address to which delivery errors are sent. In many cases,
this variable has the same value as $sender_address, but if, for example,
an incoming message to a mailing list has been expanded, $return_path may
have been changed to contain the address of the list maintainer.
</p>
<p>
$sender_address: The sender address that was received in the envelope of
the message. This is not necessarily the same as the contents of the <span class="docbook_emphasis">From:</span>
or <span class="docbook_emphasis">Sender:</span> header lines. For delivery error messages (“bounce messages”)
there is no sender address, and this variable is empty.
</p>
<p>
$tod_full: A full version of the time and date, for example: Wed, 18 Oct
1995 09:51:40 +0100. The timezone is always given as a numerical offset from
GMT.
</p>
<p>
$tod_log: The time and date in the format used for writing Exim’s log files,
without the timezone, for example: 1995-10-12 15:32:29.
</p>
<p>
$tod_zone: The local timezone offset, for example: +0100.
</p>
</div>
<div class="section">
<h3 id="SECTheadervariables" class="">5. Header variables</h3>
<p>
There is a special set of expansion variables containing the header lines of
the message being processed. These variables have names beginning with
$header_ followed by the name of the header line, terminated by a colon.
For example,
</p>
<div class="docbook_literallayout"><pre>
$header_from:
$header_subject:
</pre></div>
<p>
The whole item, including the terminating colon, is replaced by the contents of
the message header line. If there is more than one header line with the same
name, their contents are concatenated. For header lines whose data consists of
a list of addresses (for example, <span class="docbook_emphasis">From:</span> and <span class="docbook_emphasis">To:</span>), a comma and newline
is inserted between each set of data. For all other header lines, just a
newline is used.
</p>
<p>
Leading and trailing white space is removed from header line data, and if there
are any MIME “words” that are encoded as defined by RFC 2047 (because they
contain non-ASCII characters), they are decoded and translated, if possible, to
a local character set. Translation is attempted only on operating systems that
have the <span class="docbook_function">iconv()</span> function. This makes the header line look the same as it
would when displayed by an MUA. The default character set is ISO-8859-1, but
this can be changed by means of the <span class="docbook_command">headers</span> command (see below).
</p>
<p>
If you want to see the actual characters that make up a header line, you can
specify $rheader_ instead of $header_. This inserts the “raw”
header line, unmodified.
</p>
<p>
There is also an intermediate form, requested by $bheader_, which removes
leading and trailing space and decodes MIME “words”, but does not do any
character translation. If an attempt to decode what looks superficially like a
MIME “word” fails, the raw string is returned. If decoding produces a binary
zero character, it is replaced by a question mark.
</p>
<p>
The capitalization of the name following $header_ is not significant.
Because any printing character except colon may appear in the name of a
message’s header (this is a requirement of RFC 2822, the document that
describes the format of a mail message) curly brackets must <span class="docbook_emphasis">not</span> be used in
this case, as they will be taken as part of the header name. Two shortcuts are
allowed in naming header variables:
</p>
<ul>
<li>
<p>
The initiating $header_, $rheader_, or $bheader_ can be
abbreviated to $h_, $rh_, or $bh_, respectively.
</p>
</li>
<li>
<p>
The terminating colon can be omitted if the next character is white space. The
white space character is retained in the expanded string. However, this is not
recommended, because it makes it easy to forget the colon when it really is
needed.
</p>
</li>
</ul>
<p>
If the message does not contain a header of the given name, an empty string is
substituted. Thus it is important to spell the names of headers correctly. Do
not use $header_Reply_to when you really mean $header_Reply-to.
</p>
</div>
<div class="section">
<h3 id="SEC20" class="">6. User variables</h3>
<p>
There are ten user variables with names $n0 – $n9 that can be
incremented by the <span class="docbook_command">add</span> command (see section <a href="filter_ch03.html#SECTadd" title="3. Exim filter files">3.10</a>). These can be
used for “scoring” messages in various ways. If Exim is configured to run a
“system filter” on every message, the values left in these variables are
copied into the variables $sn0 – $sn9 at the end of the system filter,
thus making them available to users’ filter files. How these values are used is
entirely up to the individual installation.
</p>
</div>
<div class="section">
<h3 id="SEC21" class="">7. Current directory</h3>
<p>
The contents of your filter file should not make any assumptions about the
current directory. It is best to use absolute paths for file names; you can
normally make use of the $home variable to refer to your home directory. The
<span class="docbook_command">save</span> command automatically inserts $home at the start of non-absolute
paths.
</p>
</div>
<div class="section">
<h3 id="SECTsigdel" class="">8. Significant deliveries</h3>
<p>
When in the course of delivery a message is processed by a filter file, what
happens next, that is, after the filter file has been processed, depends on
whether or not the filter sets up any <span class="docbook_emphasis">significant deliveries</span>. If at least
one significant delivery is set up, the filter is considered to have handled
the entire delivery arrangements for the current address, and no further
processing of the address takes place. If, however, no significant deliveries
are set up, Exim continues processing the current address as if there were no
filter file, and typically sets up a delivery of a copy of the message into a
local mailbox. In particular, this happens in the special case of a filter file
containing only comments.
</p>
<p>
The delivery commands <span class="docbook_command">deliver</span>, <span class="docbook_command">save</span>, and <span class="docbook_command">pipe</span> are by default
significant. However, if such a command is preceded by the word “unseen”, its
delivery is not considered to be significant. In contrast, other commands such
as <span class="docbook_command">mail</span> and <span class="docbook_command">vacation</span> do not set up significant deliveries unless
preceded by the word “seen”. The following example commands set up
significant deliveries:
</p>
<div class="docbook_literallayout"><pre>
deliver jack@beanstalk.example
pipe $home/bin/mymailscript
seen mail subject "message discarded"
seen finish
</pre></div>
<p>
The following example commands do not set up significant deliveries:
</p>
<div class="docbook_literallayout"><pre>
unseen deliver jack@beanstalk.example
unseen pipe $home/bin/mymailscript
mail subject "message discarded"
finish
</pre></div>
</div>
<div class="section">
<h3 id="SEC222" class="">9. Filter commands</h3>
<p>
The filter commands that are described in subsequent sections are listed
below, with the section in which they are described in brackets:
</p>
<table>
<tr>
<td><span class="docbook_command">add</span></td>
<td> increment a user variable (section <a href="filter_ch03.html#SECTadd" title="3. Exim filter files">3.10</a>)</td>
</tr>
<tr>
<td><span class="docbook_command">deliver</span></td>
<td> deliver to an email address (section <a href="filter_ch03.html#SECTdeliver" title="3. Exim filter files">3.11</a>)</td>
</tr>
<tr>
<td><span class="docbook_command">fail</span></td>
<td> force delivery failure (sysadmin use) (section <a href="filter_ch03.html#SECTfail" title="3. Exim filter files">3.18</a>)</td>
</tr>
<tr>
<td><span class="docbook_command">finish</span></td>
<td> end processing (section <a href="filter_ch03.html#SECTfinish" title="3. Exim filter files">3.16</a>)</td>
</tr>
<tr>
<td><span class="docbook_command">freeze</span></td>
<td> freeze message (sysadmin use) (section <a href="filter_ch03.html#SECTfreeze" title="3. Exim filter files">3.19</a>)</td>
</tr>
<tr>
<td><span class="docbook_command">headers</span></td>
<td> set the header character set (section <a href="filter_ch03.html#SECTheaders" title="3. Exim filter files">3.20</a>)</td>
</tr>
<tr>
<td><span class="docbook_command">if</span></td>
<td> test condition(s) (section <a href="filter_ch03.html#SECTif" title="3. Exim filter files">3.21</a>)</td>
</tr>
<tr>
<td><span class="docbook_command">logfile</span></td>
<td> define log file (section <a href="filter_ch03.html#SECTlog" title="3. Exim filter files">3.15</a>)</td>
</tr>
<tr>
<td><span class="docbook_command">logwrite</span></td>
<td> write to log file (section <a href="filter_ch03.html#SECTlog" title="3. Exim filter files">3.15</a>)</td>
</tr>
<tr>
<td><span class="docbook_command">mail</span></td>
<td> send a reply message (section <a href="filter_ch03.html#SECTmail" title="3. Exim filter files">3.14</a>)</td>
</tr>
<tr>
<td><span class="docbook_command">pipe</span></td>
<td> pipe to a command (section <a href="filter_ch03.html#SECTpipe" title="3. Exim filter files">3.13</a>)</td>
</tr>
<tr>
<td><span class="docbook_command">save</span></td>
<td> save to a file (section <a href="filter_ch03.html#SECTsave" title="3. Exim filter files">3.12</a>)</td>
</tr>
<tr>
<td><span class="docbook_command">testprint</span></td>
<td> print while testing (section <a href="filter_ch03.html#SECTtestprint" title="3. Exim filter files">3.17</a>)</td>
</tr>
<tr>
<td><span class="docbook_command">vacation</span></td>
<td> tailored form of <span class="docbook_command">mail</span> (section <a href="filter_ch03.html#SECTmail" title="3. Exim filter files">3.14</a>)</td>
</tr>
</table>
<p>
The <span class="docbook_command">headers</span> command has additional parameters that can be used only in a
system filter. The <span class="docbook_command">fail</span> and <span class="docbook_command">freeze</span> commands are available only when
Exim’s filtering facilities are being used as a system filter, and are
therefore usable only by the system administrator and not by ordinary users.
They are mentioned only briefly in this document; for more information, see the
main Exim specification.
</p>
</div>
<div class="section">
<h3 id="SECTadd" class="">10. The add command</h3>
<div class="docbook_literallayout"><pre>
<code class="docbook_literal"> add </code><<span class="docbook_emphasis">number</span>><code class="docbook_literal"> to </code><<span class="docbook_emphasis">user variable</span>>
<code class="docbook_literal">e.g. add 2 to n3</code>
</pre></div>
<p>
There are 10 user variables of this type, with names $n0 – $n9. Their
values can be obtained by the normal expansion syntax (for example $n3) in
other commands. At the start of filtering, these variables all contain zero.
Both arguments of the <span class="docbook_command">add</span> command are expanded before use, making it
possible to add variables to each other. Subtraction can be obtained by adding
negative numbers.
</p>
</div>
<div class="section">
<h3 id="SECTdeliver" class="">11. The deliver command</h3>
<div class="docbook_literallayout"><pre>
<code class="docbook_literal"> deliver</code> <<span class="docbook_emphasis">mail address</span>>
<code class="docbook_literal">e.g. deliver "Dr Livingstone <David@somewhere.africa.example>"</code>
</pre></div>
<p>
This command provides a forwarding operation. The delivery that it sets up is
significant unless the command is preceded by “unseen” (see section
<a href="filter_ch03.html#SECTsigdel" title="3. Exim filter files">3.8</a>). The message is sent on to the given address, exactly as
happens if the address had appeared in a traditional <span class="docbook_filename">.forward</span> file. If you
want to deliver the message to a number of different addresses, you can use
more than one <span class="docbook_command">deliver</span> command (each one may have only one address).
However, duplicate addresses are discarded.
</p>
<p>
To deliver a copy of the message to your normal mailbox, your login name can be
given as the address. Once an address has been processed by the filtering
mechanism, an identical generated address will not be so processed again, so
doing this does not cause a loop.
</p>
<p>
However, if you have a mail alias, you should <span class="docbook_emphasis">not</span> refer to it here. For
example, if the mail address <span class="docbook_emphasis">L.Gulliver</span> is aliased to <span class="docbook_emphasis">lg303</span> then all
references in Gulliver’s <span class="docbook_filename">.forward</span> file should be to <span class="docbook_emphasis">lg303</span>. A reference
to the alias will not work for messages that are addressed to that alias,
since, like <span class="docbook_filename">.forward</span> file processing, aliasing is performed only once on an
address, in order to avoid looping.
</p>
<p>
Following the new address, an optional second address, preceded by
“errors_to” may appear. This changes the address to which delivery errors on
the forwarded message will be sent. Instead of going to the message’s original
sender, they go to this new address. For ordinary users, the only value that is
permitted for this address is the user whose filter file is being processed.
For example, the user <span class="docbook_emphasis">lg303</span> whose mailbox is in the domain
<span class="docbook_emphasis">lilliput.example</span> could have a filter file that contains
</p>
<div class="docbook_literallayout"><pre>
deliver jon@elsewhere.example errors_to lg303@lilliput.example
</pre></div>
<p>
Clearly, using this feature makes sense only in situations where not all
messages are being forwarded. In particular, bounce messages must not be
forwarded in this way, as this is likely to create a mail loop if something
goes wrong.
</p>
</div>
<div class="section">
<h3 id="SECTsave" class="">12. The save command</h3>
<div class="docbook_literallayout"><pre>
<code class="docbook_literal"> save </code><<span class="docbook_emphasis">file name</span>>
<code class="docbook_literal">e.g. save $home/mail/bookfolder</code>
</pre></div>
<p>
This command specifies that a copy of the message is to be appended to the
given file (that is, the file is to be used as a mail folder). The delivery
that <span class="docbook_command">save</span> sets up is significant unless the command is preceded by
“unseen” (see section <a href="filter_ch03.html#SECTsigdel" title="3. Exim filter files">3.8</a>).
</p>
<p>
More than one <span class="docbook_command">save</span> command may be obeyed; each one causes a copy of the
message to be written to its argument file, provided they are different
(duplicate <span class="docbook_command">save</span> commands are ignored).
</p>
<p>
If the file name does not start with a / character, the contents of the
$home variable are prepended, unless it is empty, or the system
administrator has disabled this feature. In conventional configurations, this
variable is normally set in a user filter to the user’s home directory, but the
system administrator may set it to some other path. In some configurations,
$home may be unset, or prepending may be disabled, in which case a
non-absolute path name may be generated. Such configurations convert this to an
absolute path when the delivery takes place. In a system filter, $home is
never set.
</p>
<p>
The user must of course have permission to write to the file, and the writing
of the file takes place in a process that is running as the user, under the
user’s primary group. Any secondary groups to which the user may belong are not
normally taken into account, though the system administrator can configure Exim
to set them up. In addition, the ability to use this command at all is
controlled by the system administrator – it may be forbidden on some systems.
</p>
<p>
An optional mode value may be given after the file name. The value for the mode
is interpreted as an octal number, even if it does not begin with a zero. For
example:
</p>
<div class="docbook_literallayout"><pre>
save /some/folder 640
</pre></div>
<p>
This makes it possible for users to override the system-wide mode setting for
file deliveries, which is normally 600. If an existing file does not have the
correct mode, it is changed.
</p>
<p>
An alternative form of delivery may be enabled on your system, in which each
message is delivered into a new file in a given directory. If this is the case,
this functionality can be requested by giving the directory name terminated by
a slash after the <span class="docbook_command">save</span> command, for example
</p>
<div class="docbook_literallayout"><pre>
save separated/messages/
</pre></div>
<p>
There are several different formats for such deliveries; check with your system
administrator or local documentation to find out which (if any) are available
on your system. If this functionality is not enabled, the use of a path name
ending in a slash causes an error.
</p>
</div>
<div class="section">
<h3 id="SECTpipe" class="">13. The pipe command</h3>
<div class="docbook_literallayout"><pre>
<code class="docbook_literal"> pipe </code><<span class="docbook_emphasis">command</span>>
<code class="docbook_literal">e.g. pipe "$home/bin/countmail $sender_address"</code>
</pre></div>
<p>
This command specifies that the message is to be delivered to the specified
command using a pipe. The delivery that it sets up is significant unless the
command is preceded by “unseen” (see section <a href="filter_ch03.html#SECTsigdel" title="3. Exim filter files">3.8</a>). Remember,
however, that no deliveries are done while the filter is being processed. All
deliveries happen later on. Therefore, the result of running the pipe is not
available to the filter.
</p>
<p>
When the deliveries are done, a separate process is run, and a copy of the
message is passed on its standard input. The process runs as the user, under
the user’s primary group. Any secondary groups to which the user may belong are
not normally taken into account, though the system administrator can configure
Exim to set them up. More than one <span class="docbook_command">pipe</span> command may appear; each one causes
a copy of the message to be written to its argument pipe, provided they are
different (duplicate <span class="docbook_command">pipe</span> commands are ignored).
</p>
<p>
When the time comes to transport the message, the command supplied to <span class="docbook_command">pipe</span>
is split up by Exim into a command name and a number of arguments. These are
delimited by white space except for arguments enclosed in double quotes, in
which case backslash is interpreted as an escape, or in single quotes, in which
case no escaping is recognized. Note that as the whole command is normally
supplied in double quotes, a second level of quoting is required for internal
double quotes. For example:
</p>
<div class="docbook_literallayout"><pre>
pipe "$home/myscript \"size is $message_size\""
</pre></div>
<p>
String expansion is performed on the separate components after the line has
been split up, and the command is then run directly by Exim; it is not run
under a shell. Therefore, substitution cannot change the number of arguments,
nor can quotes, backslashes or other shell metacharacters in variables cause
confusion.
</p>
<p>
Documentation for some programs that are normally run via this kind of pipe
often suggest that the command should start with
</p>
<div class="docbook_literallayout"><pre>
IFS=" "
</pre></div>
<p>
This is a shell command, and should <span class="docbook_emphasis">not</span> be present in Exim filter files,
since it does not normally run the command under a shell.
</p>
<p>
However, there is an option that the administrator can set to cause a shell to
be used. In this case, the entire command is expanded as a single string and
passed to the shell for interpretation. It is recommended that this be avoided
if at all possible, since it can lead to problems when inserted variables
contain shell metacharacters.
</p>
<p>
The default PATH set up for the command is determined by the system
administrator, usually containing at least <span class="docbook_filename">/bin</span> and <span class="docbook_filename">/usr/bin</span> so that
common commands are available without having to specify an absolute file name.
However, it is possible for the system administrator to restrict the pipe
facility so that the command name must not contain any / characters, and must
be found in one of the directories in the configured PATH. It is also possible
for the system administrator to lock out the use of the <span class="docbook_command">pipe</span> command
altogether.
</p>
<p>
When the command is run, a number of environment variables are set up. The
complete list for pipe deliveries may be found in the Exim reference manual.
Those that may be useful for pipe deliveries from user filter files are:
</p>
<div class="docbook_literallayout"><pre>
<code class="docbook_literal">DOMAIN </code> the domain of the address
<code class="docbook_literal">HOME </code> your home directory
<code class="docbook_literal">LOCAL_PART </code> see below
<code class="docbook_literal">LOCAL_PART_PREFIX </code> see below
<code class="docbook_literal">LOCAL_PART_SUFFIX </code> see below
<code class="docbook_literal">LOGNAME </code> your login name
<code class="docbook_literal">MESSAGE_ID </code> the unique id of the message
<code class="docbook_literal">PATH </code> the command search path
<code class="docbook_literal">RECIPIENT </code> the complete recipient address
<code class="docbook_literal">SENDER </code> the sender of the message
<code class="docbook_literal">SHELL </code> <code class="docbook_literal">/bin/sh</code>
<code class="docbook_literal">USER </code> see below
</pre></div>
<p>
LOCAL_PART, LOGNAME, and USER are all set to the same value, namely, your login
id. LOCAL_PART_PREFIX and LOCAL_PART_SUFFIX may be set if Exim is configured to
recognize prefixes or suffixes in the local parts of addresses. For example, a
message addressed to <span class="docbook_emphasis">pat-suf2@domain.example</span> may cause the filter for user
<span class="docbook_emphasis">pat</span> to be run. If this sets up a pipe delivery, LOCAL_PART_SUFFIX is
<code class="docbook_literal">-suf2</code> when the pipe command runs. The system administrator has to configure
Exim specially for this feature to be available.
</p>
<p>
If you run a command that is a shell script, be very careful in your use of
data from the incoming message in the commands in your script. RFC 2822 is very
generous in the characters that are permitted to appear in mail addresses, and
in particular, an address may begin with a vertical bar or a slash. For this
reason you should always use quotes round any arguments that involve data from
the message, like this:
</p>
<div class="docbook_literallayout"><pre>
/some/command '$SENDER'
</pre></div>
<p>
so that inserted shell meta-characters do not cause unwanted effects.
</p>
<p>
Remember that, as was explained earlier, the pipe command is not run at the
time the filter file is interpreted. The filter just defines what deliveries
are required for one particular addressee of a message. The deliveries
themselves happen later, once Exim has decided everything that needs to be done
for the message.
</p>
<p>
A consequence of this is that you cannot inspect the return code from the pipe
command from within the filter. Nevertheless, the code returned by the command
is important, because Exim uses it to decide whether the delivery has succeeded
or failed.
</p>
<p>
The command should return a zero completion code if all has gone well. Most
non-zero codes are treated by Exim as indicating a failure of the pipe. This is
treated as a delivery failure, causing the message to be returned to its
sender. However, there are some completion codes that are treated as temporary
errors. The message remains on Exim’s spool disk, and the delivery is tried
again later, though it will ultimately time out if the delivery failures go on
too long. The completion codes to which this applies can be specified by the
system administrator; the default values are 73 and 75.
</p>
<p>
The pipe command should not normally write anything to its standard output or
standard error file descriptors. If it does, whatever is written is normally
returned to the sender of the message as a delivery error, though this action
can be varied by the system administrator.
</p>
</div>
<div class="section">
<h3 id="SECTmail" class="">14. Mail commands</h3>
<p>
There are two commands that cause the creation of a new mail message, neither
of which count as a significant delivery unless the command is preceded by the
word “seen” (see section <a href="filter_ch03.html#SECTsigdel" title="3. Exim filter files">3.8</a>). This is a powerful facility, but
it should be used with care, because of the danger of creating infinite
sequences of messages. The system administrator can forbid the use of these
commands altogether.
</p>
<p>
To help prevent runaway message sequences, these commands have no effect when
the incoming message is a bounce (delivery error) message, and messages sent by
this means are treated as if they were reporting delivery errors. Thus, they
should never themselves cause a bounce message to be returned. The basic
mail-sending command is
</p>
<div class="docbook_literallayout"><pre>
<code class="docbook_literal">mail [to </code><<span class="docbook_emphasis">address-list</span>><code class="docbook_literal">]</code>
<code class="docbook_literal"> [cc </code><<span class="docbook_emphasis">address-list</span>><code class="docbook_literal">]</code>
<code class="docbook_literal"> [bcc </code><<span class="docbook_emphasis">address-list</span>><code class="docbook_literal">]</code>
<code class="docbook_literal"> [from </code><<span class="docbook_emphasis">address</span>><code class="docbook_literal">]</code>
<code class="docbook_literal"> [reply_to </code><<span class="docbook_emphasis">address</span>><code class="docbook_literal">]</code>
<code class="docbook_literal"> [subject </code><<span class="docbook_emphasis">text</span>><code class="docbook_literal">]</code>
<code class="docbook_literal"> [extra_headers </code><<span class="docbook_emphasis">text</span>><code class="docbook_literal">]</code>
<code class="docbook_literal"> [text </code><<span class="docbook_emphasis">text</span>><code class="docbook_literal">]</code>
<code class="docbook_literal"> [[expand] file </code><<span class="docbook_emphasis">filename</span>><code class="docbook_literal">]</code>
<code class="docbook_literal"> [return message]</code>
<code class="docbook_literal"> [log </code><<span class="docbook_emphasis">log file name</span>><code class="docbook_literal">]</code>
<code class="docbook_literal"> [once </code><<span class="docbook_emphasis">note file name</span>><code class="docbook_literal">]</code>
<code class="docbook_literal"> [once_repeat </code><<span class="docbook_emphasis">time interval</span>><code class="docbook_literal">]</code>
<code class="docbook_literal">e.g. mail text "Your message about $h_subject: has been received"</code>
</pre></div>
<p>
Each <<span class="docbook_emphasis">address-list</span>> can contain a number of addresses, separated by commas,
in the format of a <span class="docbook_emphasis">To:</span> or <span class="docbook_emphasis">Cc:</span> header line. In fact, the text you supply
here is copied exactly into the appropriate header line. It may contain
additional information as well as email addresses. For example:
</p>
<div class="docbook_literallayout"><pre>
mail to "Julius Caesar <jc@rome.example>, \
<ma@rome.example> (Mark A.)"
</pre></div>
<p>
Similarly, the texts supplied for <span class="docbook_option">from</span> and <span class="docbook_option">reply_to</span> are copied into
their respective header lines.
</p>
<p>
As a convenience for use in one common case, there is also a command called
<span class="docbook_command">vacation</span>. It behaves in the same way as <span class="docbook_command">mail</span>, except that the defaults
for the <span class="docbook_option">subject</span>, <span class="docbook_option">file</span>, <span class="docbook_option">log</span>, <span class="docbook_option">once</span>, and <span class="docbook_option">once_repeat</span> options
are
</p>
<div class="docbook_literallayout"><pre>
subject "On vacation"
expand file .vacation.msg
log .vacation.log
once .vacation
once_repeat 7d
</pre></div>
<p>
respectively. These are the same file names and repeat period used by the
traditional Unix <span class="docbook_command">vacation</span> command. The defaults can be overridden by
explicit settings, but if a file name is given its contents are expanded only
if explicitly requested.
</p>
<p>
<span class="docbook_emphasis">Warning</span>: The <span class="docbook_command">vacation</span> command should always be used conditionally,
subject to at least the <span class="docbook_command">personal</span> condition (see section <a href="filter_ch03.html#SECTpersonal" title="3. Exim filter files">3.27</a>
below) so as not to send automatic replies to non-personal messages from
mailing lists or elsewhere. Sending an automatic response to a mailing list or
a mailing list manager is an Internet Sin.
</p>
<p>
For both commands, the key/value argument pairs can appear in any order. At
least one of <span class="docbook_option">text</span> or <span class="docbook_option">file</span> must appear (except with <span class="docbook_command">vacation</span>, where
there is a default for <span class="docbook_option">file</span>); if both are present, the text string appears
first in the message. If <span class="docbook_option">expand</span> precedes <span class="docbook_option">file</span>, each line of the file is
subject to string expansion before it is included in the message.
</p>
<p>
Several lines of text can be supplied to <span class="docbook_option">text</span> by including the escape
sequence “\n” in the string wherever a newline is required. If the command is
output during filter file testing, newlines in the text are shown as “\n”.
</p>
<p>
Note that the keyword for creating a <span class="docbook_emphasis">Reply-To:</span> header is <span class="docbook_option">reply_to</span>,
because Exim keywords may contain underscores, but not hyphens. If the <span class="docbook_option">from</span>
keyword is present and the given address does not match the user who owns the
forward file, Exim normally adds a <span class="docbook_emphasis">Sender:</span> header to the message, though it
can be configured not to do this.
</p>
<p>
The <span class="docbook_option">extra_headers</span> keyword allows you to add custom header lines to the
message. The text supplied must be one or more syntactically valid RFC 2822
header lines. You can use “\n” within quoted text to specify newlines between
headers, and also to define continued header lines. For example:
</p>
<div class="docbook_literallayout"><pre>
extra_headers "h1: first\nh2: second\n continued\nh3: third"
</pre></div>
<p>
No newline should appear at the end of the final header line.
</p>
<p>
If no <span class="docbook_option">to</span> argument appears, the message is sent to the address in the
$reply_address variable (see section <a href="filter_ch03.html#SECTfilterstringexpansion" title="3. Exim filter files">3.3</a> above).
An <span class="docbook_emphasis">In-Reply-To:</span> header is automatically included in the created message,
giving a reference to the message identification of the incoming message.
</p>
<p>
If <span class="docbook_option">return message</span> is specified, the incoming message that caused the filter
file to be run is added to the end of the message, subject to a maximum size
limitation.
</p>
<p>
If a log file is specified, a line is added to it for each message sent.
</p>
<p>
If a <span class="docbook_option">once</span> file is specified, it is used to hold a database for remembering
who has received a message, and no more than one message is ever sent to any
particular address, unless <span class="docbook_option">once_repeat</span> is set. This specifies a time
interval after which another copy of the message is sent. The interval is
specified as a sequence of numbers, each followed by the initial letter of one
of “seconds”, “minutes”, “hours”, “days”, or “weeks”. For example,
</p>
<div class="docbook_literallayout"><pre>
once_repeat 5d4h
</pre></div>
<p>
causes a new message to be sent if at least 5 days and 4 hours have elapsed
since the last one was sent. There must be no white space in a time interval.
</p>
<p>
Commonly, the file name specified for <span class="docbook_option">once</span> is used as the base name for
direct-access (DBM) file operations. There are a number of different DBM
libraries in existence. Some operating systems provide one as a default, but
even in this case a different one may have been used when building Exim. With
some DBM libraries, specifying <span class="docbook_option">once</span> results in two files being created,
with the suffixes <span class="docbook_filename">.dir</span> and <span class="docbook_filename">.pag</span> being added to the given name. With
some others a single file with the suffix <span class="docbook_filename">.db</span> is used, or the name is used
unchanged.
</p>
<p>
Using a DBM file for implementing the <span class="docbook_option">once</span> feature means that the file
grows as large as necessary. This is not usually a problem, but some system
administrators want to put a limit on it. The facility can be configured not to
use a DBM file, but instead, to use a regular file with a maximum size. The
data in such a file is searched sequentially, and if the file fills up, the
oldest entry is deleted to make way for a new one. This means that some
correspondents may receive a second copy of the message after an unpredictable
interval. Consult your local information to see if your system is configured
this way.
</p>
<p>
More than one <span class="docbook_command">mail</span> or <span class="docbook_command">vacation</span> command may be obeyed in a single filter
run; they are all honoured, even when they are to the same recipient.
</p>
</div>
<div class="section">
<h3 id="SECTlog" class="">15. Logging commands</h3>
<p>
A log can be kept of actions taken by a filter file. This facility is normally
available in conventional configurations, but there are some situations where
it might not be. Also, the system administrator may choose to disable it. Check
your local information if in doubt.
</p>
<p>
Logging takes place while the filter file is being interpreted. It does not
queue up for later like the delivery commands. The reason for this is so that a
log file need be opened only once for several write operations. There are two
commands, neither of which constitutes a significant delivery. The first
defines a file to which logging output is subsequently written:
</p>
<div class="docbook_literallayout"><pre>
<code class="docbook_literal"> logfile </code><<span class="docbook_emphasis">file name</span>>
<code class="docbook_literal">e.g. logfile $home/filter.log</code>
</pre></div>
<p>
The file name must be fully qualified. You can use $home, as in this
example, to refer to your home directory. The file name may optionally be
followed by a mode for the file, which is used if the file has to be created.
For example,
</p>
<div class="docbook_literallayout"><pre>
logfile $home/filter.log 0644
</pre></div>
<p>
The number is interpreted as octal, even if it does not begin with a zero.
The default for the mode is 600. It is suggested that the <span class="docbook_command">logfile</span> command
normally appear as the first command in a filter file. Once a log file has
been obeyed, the <span class="docbook_command">logwrite</span> command can be used to write to it:
</p>
<div class="docbook_literallayout"><pre>
<code class="docbook_literal"> logwrite "</code><<span class="docbook_emphasis">some text string</span>><code class="docbook_literal">"</code>
<code class="docbook_literal">e.g. logwrite "$tod_log $message_id processed"</code>
</pre></div>
<p>
It is possible to have more than one <span class="docbook_command">logfile</span> command, to specify writing to
different log files in different circumstances. Writing takes place at the end
of the file, and a newline character is added to the end of each string if
there isn’t one already there. Newlines can be put in the middle of the string
by using the “\n” escape sequence. Lines from simultaneous deliveries may get
interleaved in the file, as there is no interlocking, so you should plan your
logging with this in mind. However, data should not get lost.
</p>
</div>
<div class="section">
<h3 id="SECTfinish" class="">16. The finish command</h3>
<p>
The command <span class="docbook_command">finish</span>, which has no arguments, causes Exim to stop
interpreting the filter file. This is not a significant action unless preceded
by “seen”. A filter file containing only “seen finish” is a black hole.
</p>
</div>
<div class="section">
<h3 id="SECTtestprint" class="">17. The testprint command</h3>
<p>
It is sometimes helpful to be able to print out the values of variables when
testing filter files. The command
</p>
<div class="docbook_literallayout"><pre>
<code class="docbook_literal"> testprint </code><<span class="docbook_emphasis">text</span>>
<code class="docbook_literal">e.g. testprint "home=$home reply_address=$reply_address"</code>
</pre></div>
<p>
does nothing when mail is being delivered. However, when the filtering code is
being tested by means of the <span class="docbook_option">-bf</span> option (see section <a href="filter_ch01.html#SECTtesting" title="1. Forwarding and filtering in Exim">1.3</a>
above), the value of the string is written to the standard output.
</p>
</div>
<div class="section">
<h3 id="SECTfail" class="">18. The fail command</h3>
<p>
When Exim’s filtering facilities are being used as a system filter, the
<span class="docbook_command">fail</span> command is available, to force delivery failure. Because this command
is normally usable only by the system administrator, and not enabled for use by
ordinary users, it is described in more detail in the main Exim specification
rather than in this document.
</p>
</div>
<div class="section">
<h3 id="SECTfreeze" class="">19. The freeze command</h3>
<p>
When Exim’s filtering facilities are being used as a system filter, the
<span class="docbook_command">freeze</span> command is available, to freeze a message on the queue. Because this
command is normally usable only by the system administrator, and not enabled
for use by ordinary users, it is described in more detail in the main Exim
specification rather than in this document.
</p>
</div>
<div class="section">
<h3 id="SECTheaders" class="">20. The headers command</h3>
<p>
The <span class="docbook_command">headers</span> command can be used to change the target character set that is
used when translating the contents of encoded header lines for insertion by the
$header_ mechanism (see section <a href="filter_ch03.html#SECTheadervariables" title="3. Exim filter files">3.5</a> above). The
default can be set in the Exim configuration; if not specified, ISO-8859-1 is
used. The only currently supported format for the <span class="docbook_command">headers</span> command in user
filters is as in this example:
</p>
<div class="docbook_literallayout"><pre>
headers charset "UTF-8"
</pre></div>
<p>
That is, <span class="docbook_command">headers</span> is followed by the word “charset” and then the name of a
character set. This particular example would be useful if you wanted to compare
the contents of a header to a UTF-8 string.
</p>
<p>
In system filter files, the <span class="docbook_command">headers</span> command can be used to add or remove
header lines from the message. These features are described in the main Exim
specification.
</p>
</div>
<div class="section">
<h3 id="SECTif" class="">21. Obeying commands conditionally</h3>
<p>
Most of the power of filtering comes from the ability to test conditions and
obey different commands depending on the outcome. The <span class="docbook_command">if</span> command is used to
specify conditional execution, and its general form is
</p>
<div class="docbook_literallayout"><pre>
<code class="docbook_literal">if </code><<span class="docbook_emphasis">condition</span>>
<code class="docbook_literal">then </code><<span class="docbook_emphasis">commands</span>>
<code class="docbook_literal">elif </code><<span class="docbook_emphasis">condition</span>>
<code class="docbook_literal">then </code><<span class="docbook_emphasis">commands</span>>
<code class="docbook_literal">else </code><<span class="docbook_emphasis">commands</span>>
<code class="docbook_literal">endif</code>
</pre></div>
<p>
There may be any number of <span class="docbook_command">elif</span> and <span class="docbook_command">then</span> sections (including none) and
the <span class="docbook_command">else</span> section is also optional. Any number of commands, including nested
<span class="docbook_command">if</span> commands, may appear in any of the <<span class="docbook_emphasis">commands</span>> sections.
</p>
<p>
Conditions can be combined by using the words <span class="docbook_command">and</span> and <span class="docbook_command">or</span>, and round
brackets (parentheses) can be used to specify how several conditions are to
combine. Without brackets, <span class="docbook_command">and</span> is more binding than <span class="docbook_command">or</span>. For example:
</p>
<div class="docbook_literallayout"><pre>
if
$h_subject: contains "Make money" or
$h_precedence: is "junk" or
($h_sender: matches ^\\d{8}@ and not personal) or
$message_body contains "this is not spam"
then
seen finish
endif
</pre></div>
<p>
A condition can be preceded by <span class="docbook_command">not</span> to negate it, and there are also some
negative forms of condition that are more English-like.
</p>
</div>
<div class="section">
<h3 id="SEC23" class="">22. String testing conditions</h3>
<p>
There are a number of conditions that operate on text strings, using the words
“begins”, “ends”, “is”, “contains” and “matches”. If you want to
apply the same test to more than one header line, you can easily concatenate
them into a single string for testing, as in this example:
</p>
<div class="docbook_literallayout"><pre>
if "$h_to:, $h_cc:" contains me@domain.example then ...
</pre></div>
<p>
If a string-testing condition name is written in lower case, the testing
of letters is done without regard to case; if it is written in upper case
(for example, “CONTAINS”), the case of letters is taken into account.
</p>
<div class="docbook_literallayout"><pre>
<code class="docbook_literal"> </code><<span class="docbook_emphasis">text1</span>><code class="docbook_literal"> begins </code><<span class="docbook_emphasis">text2</span>>
<code class="docbook_literal"> </code><<span class="docbook_emphasis">text1</span>><code class="docbook_literal"> does not begin </code><<span class="docbook_emphasis">text2</span>>
<code class="docbook_literal">e.g. $header_from: begins "Friend@"</code>
</pre></div>
<p>
A “begins” test checks for the presence of the second string at the start of
the first, both strings having been expanded.
</p>
<div class="docbook_literallayout"><pre>
<code class="docbook_literal"> </code><<span class="docbook_emphasis">text1</span>><code class="docbook_literal"> ends </code><<span class="docbook_emphasis">text2</span>>
<code class="docbook_literal"> </code><<span class="docbook_emphasis">text1</span>><code class="docbook_literal"> does not end </code><<span class="docbook_emphasis">text2</span>>
<code class="docbook_literal">e.g. $header_from: ends "public.com.example"</code>
</pre></div>
<p>
An “ends” test checks for the presence of the second string at the end of
the first, both strings having been expanded.
</p>
<div class="docbook_literallayout"><pre>
<code class="docbook_literal"> </code><<span class="docbook_emphasis">text1</span>><code class="docbook_literal"> is </code><<span class="docbook_emphasis">text2</span>>
<code class="docbook_literal"> </code><<span class="docbook_emphasis">text1</span>><code class="docbook_literal"> is not </code><<span class="docbook_emphasis">text2</span>>
<code class="docbook_literal">e.g. $local_part_suffix is "-foo"</code>
</pre></div>
<p>
An “is” test does an exact match between the strings, having first expanded
both strings.
</p>
<div class="docbook_literallayout"><pre>
<code class="docbook_literal"> </code><<span class="docbook_emphasis">text1</span>><code class="docbook_literal"> contains </code><<span class="docbook_emphasis">text2</span>>
<code class="docbook_literal"> </code><<span class="docbook_emphasis">text1</span>><code class="docbook_literal"> does not contain </code><<span class="docbook_emphasis">text2</span>>
<code class="docbook_literal">e.g. $header_subject: contains "evolution"</code>
</pre></div>
<p>
A “contains” test does a partial string match, having expanded both strings.
</p>
<div class="docbook_literallayout"><pre>
<code class="docbook_literal"> </code><<span class="docbook_emphasis">text1</span>><code class="docbook_literal"> matches </code><<span class="docbook_emphasis">text2</span>>
<code class="docbook_literal"> </code><<span class="docbook_emphasis">text1</span>><code class="docbook_literal"> does not match </code><<span class="docbook_emphasis">text2</span>>
<code class="docbook_literal">e.g. $sender_address matches "(bill|john)@"</code>
</pre></div>
<p>
For a “matches” test, after expansion of both strings, the second one is
interpreted as a regular expression. Exim uses the PCRE regular expression
library, which provides regular expressions that are compatible with Perl.
</p>
<p>
The match succeeds if the regular expression matches any part of the first
string. If you want a regular expression to match only at the start or end of
the subject string, you must encode that requirement explicitly, using the
<code class="docbook_literal">^</code> or <code class="docbook_literal">$</code> metacharacters. The above example, which is not so constrained,
matches all these addresses:
</p>
<div class="docbook_literallayout"><pre>
bill@test.example
john@some.example
spoonbill@example.com
littlejohn@example.com
</pre></div>
<p>
To match only the first two, you could use this:
</p>
<div class="docbook_literallayout"><pre>
if $sender_address matches "^(bill|john)@" then ...
</pre></div>
<p>
Care must be taken if you need a backslash in a regular expression, because
backslashes are interpreted as escape characters both by the string expansion
code and by Exim’s normal processing of strings in quotes. For example, if you
want to test the sender address for a domain ending in <span class="docbook_emphasis">.com</span> the regular
expression is
</p>
<div class="docbook_literallayout"><pre>
\.com$
</pre></div>
<p>
The backslash and dollar sign in that expression have to be escaped when used
in a filter command, as otherwise they would be interpreted by the expansion
code. Thus, what you actually write is
</p>
<div class="docbook_literallayout"><pre>
if $sender_address matches \\.com\$
</pre></div>
<p>
An alternative way of handling this is to make use of the <code class="docbook_literal">\N</code> expansion
flag for suppressing expansion:
</p>
<div class="docbook_literallayout"><pre>
if $sender_address matches \N\.com$\N
</pre></div>
<p>
Everything between the two occurrences of <code class="docbook_literal">\N</code> is copied without change by
the string expander (and in fact you do not need the final one, because it is
at the end of the string). If the regular expression is given in quotes
(mandatory only if it contains white space) you have to write either
</p>
<div class="docbook_literallayout"><pre>
if $sender_address matches "\\\\.com\\$"
</pre></div>
<p>
or
</p>
<div class="docbook_literallayout"><pre>
if $sender_address matches "\\N\\.com$\\N"
</pre></div>
<p>
If the regular expression contains bracketed sub-expressions, numeric
variable substitutions such as $1 can be used in the subsequent actions
after a successful match. If the match fails, the values of the numeric
variables remain unchanged. Previous values are not restored after <span class="docbook_command">endif</span>.
In other words, only one set of values is ever available. If the condition
contains several sub-conditions connected by <span class="docbook_command">and</span> or <span class="docbook_command">or</span>, it is the
strings extracted from the last successful match that are available in
subsequent actions. Numeric variables from any one sub-condition are also
available for use in subsequent sub-conditions, because string expansion of a
condition occurs just before it is tested.
</p>
</div>
<div class="section">
<h3 id="SEC24" class="">23. Numeric testing conditions</h3>
<p>
The following conditions are available for performing numerical tests:
</p>
<div class="docbook_literallayout"><pre>
<code class="docbook_literal"> </code><<span class="docbook_emphasis">number1</span>><code class="docbook_literal"> is above </code><<span class="docbook_emphasis">number2</span>>
<code class="docbook_literal"> </code><<span class="docbook_emphasis">number1</span>><code class="docbook_literal"> is not above </code><<span class="docbook_emphasis">number2</span>>
<code class="docbook_literal"> </code><<span class="docbook_emphasis">number1</span>><code class="docbook_literal"> is below </code><<span class="docbook_emphasis">number2</span>>
<code class="docbook_literal"> </code><<span class="docbook_emphasis">number1</span>><code class="docbook_literal"> is not below </code><<span class="docbook_emphasis">number2</span>>
<code class="docbook_literal">e.g. $message_size is not above 10k</code>
</pre></div>
<p>
The <<span class="docbook_emphasis">number</span>> arguments must expand to strings of digits, optionally
followed by one of the letters K or M (upper case or lower case) which cause
multiplication by 1024 and 1024x1024 respectively.
</p>
</div>
<div class="section">
<h3 id="SEC25" class="">24. Testing for significant deliveries</h3>
<p>
You can use the <span class="docbook_command">delivered</span> condition to test whether or not any previously
obeyed filter commands have set up a significant delivery. For example:
</p>
<div class="docbook_literallayout"><pre>
if not delivered then save mail/anomalous endif
</pre></div>
<p>
“Delivered” is perhaps a poor choice of name for this condition, because the
message has not actually been delivered; rather, a delivery has been set up for
later processing.
</p>
</div>
<div class="section">
<h3 id="SEC26" class="">25. Testing for error messages</h3>
<p>
The condition <span class="docbook_command">error_message</span> is true if the incoming message is a bounce
(mail delivery error) message. Putting the command
</p>
<div class="docbook_literallayout"><pre>
if error_message then finish endif
</pre></div>
<p>
at the head of your filter file is a useful insurance against things going
wrong in such a way that you cannot receive delivery error reports. <span class="docbook_emphasis">Note</span>:
<span class="docbook_command">error_message</span> is a condition, not an expansion variable, and therefore is
not preceded by <code class="docbook_literal">$</code>.
</p>
</div>
<div class="section">
<h3 id="SEC27" class="">26. Testing a list of addresses</h3>
<p>
There is a facility for looping through a list of addresses and applying a
condition to each of them. It takes the form
</p>
<div class="docbook_literallayout"><pre>
<code class="docbook_literal">foranyaddress </code><<span class="docbook_emphasis">string</span>><code class="docbook_literal"> (</code><<span class="docbook_emphasis">condition</span>><code class="docbook_literal">)</code>
</pre></div>
<p>
where <<span class="docbook_emphasis">string</span>> is interpreted as a list of RFC 2822 addresses, as in a
typical header line, and <<span class="docbook_emphasis">condition</span>> is any valid filter condition or
combination of conditions. The “group” syntax that is defined for certain
header lines that contain addresses is supported.
</p>
<p>
The parentheses surrounding the condition are mandatory, to delimit it from
possible further sub-conditions of the enclosing <span class="docbook_command">if</span> command. Within the
condition, the expansion variable $thisaddress is set to the non-comment
portion of each of the addresses in the string in turn. For example, if the
string is
</p>
<div class="docbook_literallayout"><pre>
B.Simpson <bart@sfld.example>, lisa@sfld.example (his sister)
</pre></div>
<p>
then $thisaddress would take on the values <code class="docbook_literal">bart@sfld.example</code> and
<code class="docbook_literal">lisa@sfld.example</code> in turn.
</p>
<p>
If there are no valid addresses in the list, the whole condition is false. If
the internal condition is true for any one address, the overall condition is
true and the loop ends. If the internal condition is false for all addresses in
the list, the overall condition is false. This example tests for the presence
of an eight-digit local part in any address in a <span class="docbook_emphasis">To:</span> header:
</p>
<div class="docbook_literallayout"><pre>
if foranyaddress $h_to: ( $thisaddress matches ^\\d{8}@ ) then ...
</pre></div>
<p>
When the overall condition is true, the value of $thisaddress in the
commands that follow <span class="docbook_command">then</span> is the last value it took on inside the loop. At
the end of the <span class="docbook_command">if</span> command, the value of $thisaddress is reset to what it
was before. It is best to avoid the use of multiple occurrences of
<span class="docbook_command">foranyaddress</span>, nested or otherwise, in a single <span class="docbook_command">if</span> command, if the
value of $thisaddress is to be used afterwards, because it isn’t always
clear what the value will be. Nested <span class="docbook_command">if</span> commands should be used instead.
</p>
<p>
Header lines can be joined together if a check is to be applied to more than
one of them. For example:
</p>
<div class="docbook_literallayout"><pre>
if foranyaddress $h_to:,$h_cc: ....
</pre></div>
<p>
This scans through the addresses in both the <span class="docbook_emphasis">To:</span> and the <span class="docbook_emphasis">Cc:</span> headers.
</p>
</div>
<div class="section">
<h3 id="SECTpersonal" class="">27. Testing for personal mail</h3>
<p>
A common requirement is to distinguish between incoming personal mail and mail
from a mailing list, or from a robot or other automatic process (for example, a
bounce message). In particular, this test is normally required for “vacation
messages”.
</p>
<p>
The <span class="docbook_command">personal</span> condition checks that the message is not a bounce message and
that the current user’s email address appears in the <span class="docbook_emphasis">To:</span> header. It also
checks that the sender is not the current user or one of a number of common
daemons, and that there are no header lines starting <span class="docbook_emphasis">List-</span> in the message.
Finally, it checks the content of the <span class="docbook_emphasis">Precedence:</span> header line, if there is
one.
</p>
<p>
You should always use the <span class="docbook_command">personal</span> condition when generating automatic
responses. This example shows the use of <span class="docbook_command">personal</span> in a filter file that is
sending out vacation messages:
</p>
<div class="docbook_literallayout"><pre>
if personal then
mail to $reply_address
subject "I am on holiday"
file $home/vacation/message
once $home/vacation/once
once_repeat 10d
endif
</pre></div>
<p>
It is tempting, when writing commands like the above, to quote the original
subject in the reply. For example:
</p>
<div class="docbook_literallayout"><pre>
subject "Re: $h_subject:"
</pre></div>
<p>
There is a danger in doing this, however. It may allow a third party to
subscribe you to an opt-in mailing list, provided that the list accepts bounce
messages as subscription confirmations. (Messages sent from filters are always
sent as bounce messages.) Well-managed lists require a non-bounce message to
confirm a subscription, so the danger is relatively small.
</p>
<p>
If prefixes or suffixes are in use for local parts – something which depends
on the configuration of Exim (see section <a href="filter_ch03.html#SECTmbox" title="3. Exim filter files">3.31</a> below) – the tests
for the current user are done with the full address (including the prefix and
suffix, if any) as well as with the prefix and suffix removed. If the system is
configured to rewrite local parts of mail addresses, for example, to rewrite
<code class="docbook_literal">dag46</code> as <code class="docbook_literal">Dirk.Gently</code>, the rewritten form of the address is also used in
the tests.
</p>
</div>
<div class="section">
<h3 id="SEC28" class="">28. Alias addresses for the personal condition</h3>
<p>
It is quite common for people who have mail accounts on a number of different
systems to forward all their mail to one system, and in this case a check for
personal mail should test all their various mail addresses. To allow for this,
the <span class="docbook_command">personal</span> condition keyword can be followed by
</p>
<div class="docbook_literallayout"><pre>
<code class="docbook_literal">alias </code><<span class="docbook_emphasis">address</span>>
</pre></div>
<p>
any number of times, for example:
</p>
<div class="docbook_literallayout"><pre>
if personal alias smith@else.where.example
alias jones@other.place.example
then ...
</pre></div>
<p>
The alias addresses are treated as alternatives to the current user’s email
address when testing the contents of header lines.
</p>
</div>
<div class="section">
<h3 id="SEC29" class="">29. Details of the personal condition</h3>
<p>
The basic <span class="docbook_command">personal</span> test is roughly equivalent to the following:
</p>
<div class="docbook_literallayout"><pre>
not error_message and
$message_headers does not contain "\nList-Id:" and
$message_headers does not contain "\nList-Help:" and
$message_headers does not contain "\nList-Subscribe:" and
$message_headers does not contain "\nList-Unsubscribe:" and
$message_headers does not contain "\nList-Post:" and
$message_headers does not contain "\nList-Owner:" and
$message_headers does not contain "\nList-Archive:" and
(
"${if def:h_auto-submitted:{present}{absent}}" is "absent" or
$header_auto-submitted: is "no"
) and
$header_precedence: does not contain "bulk" and
$header_precedence: does not contain "list" and
$header_precedence: does not contain "junk" and
foranyaddress $header_to:
( $thisaddress contains "$local_part$domain" ) and
not foranyaddress $header_from:
(
$thisaddress contains "$local_part@$domain" or
$thisaddress contains "server@" or
$thisaddress contains "daemon@" or
$thisaddress contains "root@" or
$thisaddress contains "listserv@" or
$thisaddress contains "majordomo@" or
$thisaddress contains "-request@" or
$thisaddress matches "^owner-[^@]+@"
)
</pre></div>
<p>
The variable $local_part contains the local part of the mail address of
the user whose filter file is being run – it is normally your login id. The
$domain variable contains the mail domain. As explained above, if aliases
or rewriting are defined, or if prefixes or suffixes are in use, the tests for
the current user are also done with alternative addresses.
</p>
</div>
<div class="section">
<h3 id="SEC30" class="">30. Testing delivery status</h3>
<p>
There are two conditions that are intended mainly for use in system filter
files, but which are available in users’ filter files as well. The condition
<span class="docbook_command">first_delivery</span> is true if this is the first process that is attempting to
deliver the message, and false otherwise. This indicator is not reset until the
first delivery process successfully terminates; if there is a crash or a power
failure (for example), the next delivery attempt is also a “first delivery”.
</p>
<p>
In a user filter file <span class="docbook_command">first_delivery</span> will be false if there was previously
an error in the filter, or if a delivery for the user failed owing to, for
example, a quota error, or if forwarding to a remote address was deferred for
some reason.
</p>
<p>
The condition <span class="docbook_command">manually_thawed</span> is true if the message was “frozen” for
some reason, and was subsequently released by the system administrator. It is
unlikely to be of use in users’ filter files.
</p>
</div>
<div class="section">
<h3 id="SECTmbox" class="">31. Multiple personal mailboxes</h3>
<p>
The system administrator can configure Exim so that users can set up variants
on their email addresses and handle them separately. Consult your system
administrator or local documentation to see if this facility is enabled on your
system, and if so, what the details are.
</p>
<p>
The facility involves the use of a prefix or a suffix on an email address. For
example, all mail addressed to <span class="docbook_emphasis">lg303-</span><<span class="docbook_emphasis">something</span>> would be the property
of user <span class="docbook_emphasis">lg303</span>, who could determine how it was to be handled, depending on
the value of <<span class="docbook_emphasis">something</span>>.
</p>
<p>
There are two possible ways in which this can be set up. The first possibility
is the use of multiple <span class="docbook_filename">.forward</span> files. In this case, mail to <span class="docbook_emphasis">lg303-foo</span>,
for example, is handled by looking for a file called <span class="docbook_filename">.forward-foo</span> in
<span class="docbook_emphasis">lg303</span>’s home directory. If such a file does not exist, delivery fails
and the message is returned to its sender.
</p>
<p>
The alternative approach is to pass all messages through a single <span class="docbook_filename">.forward</span>
file, which must be a filter file so that it can distinguish between the
different cases by referencing the variables $local_part_prefix or
$local_part_suffix, as in the final example in section <a href="filter_ch03.html#SECTex" title="3. Exim filter files">3.33</a> below.
</p>
<p>
It is possible to configure Exim to support both schemes at once. In this case,
a specific <span class="docbook_filename">.forward-foo</span> file is first sought; if it is not found, the basic
<span class="docbook_filename">.forward</span> file is used.
</p>
<p>
The <span class="docbook_command">personal</span> test (see section <a href="filter_ch03.html#SECTpersonal" title="3. Exim filter files">3.27</a>) includes prefixes and
suffixes in its checking.
</p>
</div>
<div class="section">
<h3 id="SEC43" class="">32. Ignoring delivery errors</h3>
<p>
As was explained above, filtering just sets up addresses for delivery – no
deliveries are actually done while a filter file is active. If any of the
generated addresses subsequently suffers a delivery failure, an error message
is generated in the normal way. However, if a filter command that sets up a
delivery is preceded by the word “noerror”, errors for that delivery,
and any deliveries consequent on it (that is, from alias, forwarding, or
filter files it invokes) are ignored.
</p>
</div>
<div class="section">
<h3 id="SECTex" class="">33. Examples of Exim filter commands</h3>
<p>
Simple forwarding:
</p>
<div class="docbook_literallayout"><pre>
# Exim filter
deliver baggins@rivendell.middle-earth.example
</pre></div>
<p>
Vacation handling using traditional means, assuming that the <span class="docbook_filename">.vacation.msg</span>
and other files have been set up in your home directory:
</p>
<div class="docbook_literallayout"><pre>
# Exim filter
unseen pipe "/usr/ucb/vacation \"$local_part\""
</pre></div>
<p>
Vacation handling inside Exim, having first created a file called
<span class="docbook_filename">.vacation.msg</span> in your home directory:
</p>
<div class="docbook_literallayout"><pre>
# Exim filter
if personal then vacation endif
</pre></div>
<p>
File some messages by subject:
</p>
<div class="docbook_literallayout"><pre>
# Exim filter
if $header_subject: contains "empire" or
$header_subject: contains "foundation"
then
save $home/mail/f+e
endif
</pre></div>
<p>
Save all non-urgent messages by weekday:
</p>
<div class="docbook_literallayout"><pre>
# Exim filter
if $header_subject: does not contain "urgent" and
$tod_full matches "^(...),"
then
save $home/mail/$1
endif
</pre></div>
<p>
Throw away all mail from one site, except from postmaster:
</p>
<div class="docbook_literallayout"><pre>
# Exim filter
if $reply_address contains "@spam.site.example" and
$reply_address does not contain "postmaster@"
then
seen finish
endif
</pre></div>
<p>
Handle multiple personal mailboxes:
</p>
<div class="docbook_literallayout"><pre>
# Exim filter
if $local_part_suffix is "-foo"
then
save $home/mail/foo
elif $local_part_suffix is "-bar"
then
save $home/mail/bar
endif
</pre></div>
</div>
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