/usr/share/doc/mailfront/mailrulesx.html

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<h2><a href="mailfront.html">MailFront</a></h2>
<h2><a href="smtpfront.html">SMTP Front Ends</a></h2>
<h2><a href="mailrules.html">Mail Rules Specification</a></h2>

<h1>Mail Rules Specification vX</h1>

<hr>

<p>The current mail rules specification is lacking in several areas: <ul>

<li>There is no way to select rules based on the state of environment
variables (such as <tt>$RELAYCLIENT</tt> or <tt>$TCPREMOTEIP</tt>.

<li>There is no way to select rules based on the SMTP authentication
state.

<li>It is difficult to seperate sender processing from recipient
processing.

<li>The dictionary and CDB lookups don't support wildcarding (minor).

</ul> This document proposes an improved mail rules specification that
addresses these problems.</p>

<h2>Selection</h2>

<p>The use of mail rules is controlled by the environment variable
<tt>$MAILRULES</tt>.  This variable specifies the path to the compiled
mail rules file.  If <tt>$MAILRULES</tt> is set but the path that it
points to cannot be opened, processing will fail with a temporary error.
There is no default value -- if it is not set, mail rules processing is
disabled.</p>

<p>The rules listed are applied <i>before</i> any other sender or
recipient processing is done (such as checking against qmail's
badmailfrom file).</p>

<h2>Compiled File Format</h2>

<p>The mail rules must be compiled to a binary format.  The binary file
contains a signature header followed by rules, and terminated with a
32-bit CRC check code of all the data in the file.  All numbers are
unsigned 32-bit LSB unless otherwise indicated.  A string consisists of
a length number followed by that many bytes of data.</p>

<h3>Signature Header</h3>

<ol>

<li>Unique signature string.

<li>Rule count.

</ol>

<h3>Rule</h3>

<ol>

  <li>Rule size: total number of bytes in this rule.

  <li>Rule type: single byte code indicating what type of rule this is
  and when it should get executed.  The format of remainder of the data
  in the rule is dependant on this value. <ul>

    <li>0: Connection/Setup

    <li>1: Sender validation

    <li>2: Recipient validation

  </ul>

  <li>Conditions: count of the number of conditions (C).

  <li>(C) conditions containing:<ol>

    <li>Negation flag: single byte boolean

    <li>Comparison type: single byte code: <ul>

      <li>0: Is defined

      <li>1: Exact match

      <li>2: Pattern match

      <li>3: File lookup, whole string

      <li>4: File lookup, domain portion

      <li>5: CDB lookup, whole string

      <li>6: CDB lookup, domain portion

    </ul>

    <li>Variable name: string

    <li>Comparison value: string

  </ol>

  <li>Assignments: count of the number of assignments (A).

  <li>(A) assignments containing:<ol>

    <li>Set (1) / unset (0) flag byte

    <li>Variable name

    <li>Assigned value

  </ol>

  <li>Action: single byte code indicating the action this rule is to
  take: <ul>

    <li>0: NO-OP

    <li>1: PASS

    <li>2: ACCEPT, followed by message string.

    <li>3: DEFER, followed by message string.

    <li>4: REJECT, followed by message string.

    <li>5: DEFER-ALL, followed by message string.

    <li>6: REJECT-ALL, followed by message string.

  </ul>

  <li>Message: string containing the response message.

</ol>

<h2>Variables</h2>

<p>The following variables are internally defined. <ul>

<li><tt>authenticated</tt>: Defined if SMTP authentication has
succeeded.

<li><tt>sender</tt>: The envelope sender address.

<li><tt>recipient</tt>: The current envelope recipient address.

<li><tt>databytes</tt>: The current maximum message size.

</ul> All other variable names are taken from environment variables.</p>

<h2>Variable Substitution</h2>

<p>Response messages and assignment values undergo variable substition.
All instances of <tt>$NAME</tt> or <tt>${NAME}</tt> in these strings are
replaced with the contents of the named variable.</p>

<h2>Pattern Syntax</h2>

<p>A pattern is a string of stars and non-stars.  It matches any
concatenation of strings matched by all the stars and non-stars in the
same order.  A non-star matches itself.  A star before the end of
pattern matches any string that does not include the next character in
pattern. A star at the end of pattern matches any string.  Patterns
containing only "<tt>*</tt>" match anything.  <b>Note:</b> An empty
pattern matches <i>only</i> the empty string.</p>

<h2>Semantics</h2>

<p>Each rule is applied in the order they are listed in the rules file
until one matches.  At that point, the command that triggered the rule
search is accepted, deferred, or rejected depending on the rule type.
If the sender is not accepted, no recipients can be accepted, as usual.
As long as at least one recipient is accepted the message data may be
accepted.</p>

<h2>Text File Format</h2>

<h3>Syntax</h3>

<p>Rules are seperated into sections by one of the following lines: <dl>

  <dt><tt>[connect]</tt> <dd>Connection validation

  <dt><tt>[sender]</tt> <dd>Sender validation

  <dt><tt>[recipient]</tt> <dd>Recipient validation

</dl>

<p>Each rule in the file occupies a series of lines.  Empty lines are
used to seperate rules within the file.  Lines starting with
"<tt>#</tt>" are ignored.  The rule contains the following sections:
<ol>

<li><b>Conditions</b>: a list of zero or more conditions.  Each
condition has a format from the following list.  All conditions must be
true for the rule to execute.  A rule with no conditions always
matches. <ul>

  <li><tt>!CONDITION</tt> True if the condition (one of the below) is
  false.

  <li><tt>VAR=VALUE</tt> True if the variable named <tt>VAR</tt> is
  defined and matches "<tt>VALUE</tt>" exactly.

  <li><tt>VAR~PATTERN</tt> True if the variable <tt>VAR</tt> is defined
  and matches the pattern "<tt>PATTERN</tt>".

  <li><tt>VAR</tt> True if the variable <tt>VAR</tt> is defined (even if
  it has been assigned an empty string).

  </ul> Sender-only rules must contain the condition
  "<tt>!recipient</tt>".

<li><b>Action</b>: One of the following: <dl>

<dt><tt>:ACCEPT</tt> <dd>Accept the sender or recipient.

<dt><tt>:DEFER</tt> <dd>Reject the sender or recipient with a temporary
error code.

<dt><tt>:REJECT</tt> <dd>Reject the sender or recipient with a permanent
error code.

<dt><tt>:DEFER-ALL</tt> <dd>Reject the message with a temporary error
(rejects all past and future recipients, and resets the state).

<dt><tt>:REJECT-ALL</tt> <dd>Reject the message with a permanent error.

<dt><tt>:PASS</tt> <dd>Pass the sender or recipient on to the next
processing state (ie <tt>$RELAYCLIENT</tt> or back-end validation).

</dl> The action may be followed by another colon ("<tt>:</tt>") and a
response message that will be given to the client.  The default for this
message depends on the action.

<li><b>Assignments</b>: A list of environment variables to set or unset
as a result of matching this rule, one per line.  Each assignment is
formatted as <tt>NAME=VALUE</tt> (note, no quotes, the value ends at the
end of the line).  The special names <tt>databytes</tt>,
<tt>sender</tt>, and <tt>recipient</tt> are handled specially.
Assignment to <tt>recipient</tt> when handling a sender, and vice versa
has no effect.

</ol></p>

<h3>Escaping</h3>

<p>The following escape sequences are recognized in all the fields: <ul>

<li><tt>\n</tt> newline (replaced with a CR+LF pair on output)

<li><tt>\###</tt> character with octal value ### (exactly 3 digits)

<li><tt>\\</tt> backslash

<li><tt>\:</tt> colon

</ul></p>

<h3>Special Patterns</h3>

<p>The following patterns are treated specially: <dl>

<dt><tt>[[@<i>filename</i>]]</tt> <dd>Matches the domain portion of the
address against the control file named <tt><i>filename</i></tt>.
Typical uses would be "<tt>recipient~[[@rcpthosts]]</tt>" and
"<tt>recipient~[[@morercpthosts.cdb]]</tt>".

<dt><tt>[[<i>filename</i>]]</tt> <dd>Matches the entire address against
the control file named <tt><i>filename</i></tt>.  A typical use would be
"<tt>sender~[[badmailfrom]]</tt>".

</dl> If <tt><i>filename</i></tt> ends with <tt>.cdb</tt>, the control
file is opened as a CDB file.  Addresses are translated to lower-case
before doing CDB lookups.  Otherwise, control files are plain text
lists, with one entry per line.  Empty lines and lines starting with
"<tt>#</tt>" are ignored.  Lines starting with "<tt>@</tt>" match only
the domain portion of the address.  All comparisons are case
insensitive.  Missing CDB files are silently ignored.  Missing text
files cause an error message at startup.</p>

<h3>Examples</h3>

<h4>qmail Rules</h4>

<p>The following rules provide the functionality available in
qmail-smtpd:

<pre>
[sender]
sender~[[/var/qmail/control/badmailfrom]]
:REJECT:Sorry, your envelope sender is in my badmailfrom list (#5.7.1)

[recipient]
$RELAYCLIENT
:ACCEPT:Accepted
recipient=${recipient}$RELAYCLIENT

authenticated
:ACCEPT:Accepted

recipient~[[@/var/qmail/control/rcpthosts]]
:ACCEPT:Accepted

recipient~[[@/var/qmail/control/morercpthosts.cdb]]
:ACCEPT:Accepted

:REJECT:Sorry, that domain isn't in my list of allowed rcpthosts
</pre></p>

<h2>Missing Features</h2>

<p>The following features are absent from this description, and could be
added: <ul>

<li>Extended variable expansion: Borrow the following parameter/variable
expansion features from bash: <dl>

<dt><tt>${parameter:-word}</tt>
<dt><tt>${parameter:+word}</tt>
<dt><tt>${parameter:offset}</tt>
<dt><tt>${parameter:offset:length}</tt>
<dt><tt>${#parameter}</tt>
<dt><tt>${parameter#word}</tt>
<dt><tt>${parameter##word}</tt>
<dt><tt>${parameter%word}</tt>
<dt><tt>${parameter%%word}</tt>
<dt><tt>${parameter/pattern/string}</tt>
<dt><tt>${parameter//pattern/string}</tt>

</dl>

</ul></p>

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