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Commit d86b9f73 authored by Stuart Gathman's avatar Stuart Gathman
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Whitelists and Blacklists

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......@@ -25,7 +25,7 @@ Mascot by <a href="http://alphard.ethz.ch/hafner/lebl.htm">Christian Hafner</a>
Stuart D. Gathman</a><br>
This web page is written by Stuart D. Gathman<br>and<br>sponsored by
<a href="http://www.bmsi.com">Business Management Systems, Inc.</a> <br>
Last updated Mar 30, 2007</h4>
Last updated Aug 26, 2008</h4>
See the <a href="faq.html">FAQ</a> | <a href="http://sourceforge.net/project/showfiles.php?group_id=139894">Download now</a> |
<a href="http://bmsi.com/mailman/listinfo/pymilter">Subscribe to mailing list</a> |
......@@ -44,7 +44,9 @@ Sendmail 8.12 officially releases libmilter.
Version 8.12 seems to be more robust, and includes new privilege
separation features to enhance security. Even better, sendmail 8.13
supports socket maps, which makes <a href="pysrs.html">pysrs</a> much more
efficient and secure. I recommend upgrading.
efficient and secure. Sendmail 8.14 finally supports modifying
MAIL FROM via the milter API. Unfortunately, I haven't gotten around
to supporting that yet in python milter.
</td></tr>
</table>
......@@ -209,60 +211,8 @@ href="http://www.duh.org/cvsweb.cgi/~checkout~/pmilter/doc/milter-protocol.txt?r
<h3> Confirmed Installations </h3>
Please <a href="mailto:%73%74%75%61%72%74%40%62%6D%73%69%2E%63%6F%6D">email</a>
me if you successfully install milter on a system not mentioned below.
<p>
<table>
<tr>
<th>Operating System</th> <th>Compiler</th> <th>Python</th> <th>Sendmail</th>
<th>milter</th>
<tr>
<td>Mandrake 8.0</td><td>gcc-3.0.1</td><td>2.1.1</td><td>8.12.0</td>
<td>0.3.3</td><tr>
<td>Mandrake 8.0</td><td>gcc-2.96</td><td>2.0</td><td>8.11.2</td>
<td>0.3.6</td><tr>
<td>RedHat 6.2</td><td>egcs-1.1.2</td><td>2.2.2</td><td>8.11.6</td>
<td>0.5.4</td><tr>
<td>RedHat 7.1</td><td>gcc-2.96</td><td>?</td><td>8.12.1</td>
<td>0.3.5</td><tr>
<td>RedHat 7.3</td><td>gcc-2.96</td><td>2.2.2</td><td>8.11.6</td>
<td>0.5.5</td><tr>
<td>RedHat 7.3</td><td>gcc-2.96</td><td>2.3.3</td><td>8.13.1</td>
<td>0.7.2</td><tr>
<td>RedHat 7.3</td><td>gcc-2.96</td><td>2.4.1</td><td>8.13.5</td>
<td>0.8.4</td><tr>
<td>RedHat 8.0</td><td>gcc-3.2</td><td>2.2.1</td><td>8.12.6</td>
<td>0.5.2</td><tr>
<td>RedHat 9.0</td><td>gcc-3.2.2</td><td>2.4.1</td><td>8.13.1</td>
<td>0.8.2</td><tr>
<td>RedHat EL3</td><td>gcc-3.2.3</td><td>2.4.1</td><td>8.13.5</td>
<td>0.8.4</td><tr>
<td>Debian Linux</td><td>gcc-2.95.2</td><td>2.1.1</td><td>8.12.0</td>
<td>0.3.7</td><tr>
<td>Debian Linux</td><td>gcc-3.2.2</td><td>2.2.2</td><td>8.12.7</td>
<td>0.5.4</td><tr>
<td>AIX-4.1.5</td><td>gcc-2.95.2</td><td>2.1.1</td><td>8.11.5</td>
<td>0.3.3</td><tr>
<td>AIX-4.1.5</td><td>gcc-2.95.2</td><td>2.1.1</td><td>8.12.1</td>
<td>0.3.4</td><tr>
<td>AIX-4.1.5</td><td>gcc-2.95.2</td><td>2.1.3</td><td>8.12.3</td>
<td>0.4.2</td><tr>
<td>AIX-4.1.5</td><td>gcc-2.95.2</td><td>2.4.1</td><td>8.13.1</td>
<td>0.8.4</td><tr>
<td>Slackware 7.1</td><td>?</td><td>?</td><td>8.12.1</td>
<td>0.3.8</td><tr>
<td>Slackware 9.0</td><td>gcc-3.2.2</td><td>2.2.3</td><td>8.12.9</td>
<td>0.5.4</td><tr>
<td>OpenBSD</td><td>?</td><td>2.3.3?</td><td>8.13.1?</td>
<td>0.7.2</td><tr>
<td>SuSE 7.3</td><td>gcc-2.95.3</td><td>2.1.1</td><td>8.12.2</td>
<td>0.3.9</td><tr>
<td>FreeBSD</td><td>gcc-2.95.3</td><td>2.2.1</td><td>8.12.3</td>
<td>0.4.0</td><tr>
<td>FreeBSD</td><td>gcc-2.95.3</td><td>2.2.2</td><td>?</td>
<td>0.5.5</td><tr>
<td>FreeBSD 4.4</td><td>gcc-2.95.3</td><td>?</td><td>8.12.10</td>
<td>0.6.6</td>
</table>
me if you do <i>not</i> successfully install milter. The confirmed
installations are too numerous to list at this point.
<h2> Enough Already! </h2>
......
......@@ -82,7 +82,7 @@ to determine the official SPF policy result.
The offical SPF result is then logged in the Received-SPF header field,
but certain results are subjected to further processing to create
an effective result for policy purposes.
<p>
If the official result is 'none', we try to turn it into an effective result of
'pass' or 'fail'. First, we check for a local substitute SPF record
under the domain defined in the <code>[spf]delegate</code> configuration.
......@@ -91,12 +91,12 @@ too clueless to add their own. If there is no local substitute, we use a "best
guess" SPF record of "v=spf1 a/24 mx/24 ptr" for MAIL FROM or "v=spf1 a/24
mx/24" for HELO. In addition, a HELO that is a subdomain of MAIL FROM and
resolves to the connect IP results in an effective result of 'pass'.
<p>
If there is no local SPF record, and the effective result is still not
'pass', we check for either a valid HELO name or a valid PTR record for
the connect IP. A valid HELO or PTR cannot look like a dynamic name
as determined by the heuristic in <code>Milter.dynip</code>.
<p>
If HELO has an SPF record, and the result is anything but pass, we reject
the connection:
<pre>
......@@ -107,16 +107,16 @@ the connection:
</pre>
Note that HELO does not have any forwarding issues like MAIL FROM, and so
any result other than 'pass' or 'none' should be treated like 'fail'.
<p>
Only if nothing about the SMTP envelope can be validated does the effective
result remain 'none. I call this the "3 strikes" rule.
<p>
If the official result is 'permerror' (a syntax error in the sender's
policy), we use the 'lax' option in pyspf to try various heuristics to guess
what they really meant. For instance, the invalid mechanism "ip:1.2.3.4" is
treated as "ip4:1.2.3.4". The result of lax processing is then used
as the effective result for policy purposes.
<p>
With an effective SPF result in hand, we consult the sendmail access
database to find our receiver policy for the sender.
......@@ -159,7 +159,7 @@ SPF-Fail:abeb@adelphia.net DSN
This says to accept mail from that adelphia.net user despite the
SPF fail, but only after annoying them with a DSN about their ISP's broken
policy.
<p>
If there is no match on the full sender, the domain is checked:
<pre>
SPF-Neutral:aol.com REJECT
......@@ -168,7 +168,7 @@ This says to reject mail from AOL with an SPF result of neutral.
This means AOL users can't use their AOL address with another mail service
to send us mail. This is good because the other mail service is
likely a badly configured greeting card site or a virus.
<p>
Finally, a default policy for the result is checked. While there are program
defaults, you should have defaults in the access database for SPF results:
<pre>
......@@ -192,3 +192,58 @@ independently for each SPF result and sender combination. So aol.com:neutral
might have a really bad reputation, while aol.com:pass would be ok.
Furthermore, when a sender finally publishes an SPF policy and starts
getting SPF pass, their reputation is effectively reset.
<h2> Whitelists and Blacklists </h2>
The administrator can whitelist or blacklist senders and sending domains by
appending them to <code>${datadir}/auto_whitelist.log</code> or
<code>${datadir}/blacklist.log</code> respectively. In addition,
recipients of internal senders (except for automatic replies like vacation
messages and return receipts) are automatically whitelisted for 60 days, and
senders that fail CBV or DSN checks are automatically blacklisted for 30 days.
Whitelisted and blacklisted senders are used to automatically train the
bayesian content filter before being delivered or rejected, respectively.
<p>
Real Soon Now users will be able to maintain their own whitelist and
blacklist that applies only when they are the recipient.
<h2> Content Filter </h2>
Most messages have been rejected or delivered by now, but spammers
are always finding new places to send their junk from. For instance,
we get around 10000 emails a day, of which around 500 are first time
spam senders. A bayesian filter is trained by the whitelists and
blacklists, and scores the message. What is likely spam is either
rejected or quarantined. If the sender is an effective SPF pass,
then they get a DSN notifying them that their message has been
quarantined. (A DSN failure gets the sender auto blacklisted.)
Else, if the reject_spam option is set, the message is rejected.
Otherwise, a CBV is done (failure gets the sender auto blacklisted)
and the message is silently quarantined.
<p>
Normally, you don't want email messages to silently disappear into
a black hole, so you should set the reject_spam option. However,
if you don't want your correspondent's email to get rejected, you can
check your quarantine frequently instead.
<h3> Honeypot </h3>
You can also blacklist recipients by listing them as aliases of the
'honeypot' dspam user. These are collectively called
the honeypot. Any email to these recipients is used to train the
spam filter as spam and chalk up a reputation demerit for the sender, then
discarded. It might be a good idea to blacklist the sender if it has SPF pass
as well, but I'm afraid of accidents.
<h3> Reputation </h3>
Reputation is tracked by sending domain and effective SPF result.
The GOSSiP server tracks the spam/ham status of the last 1024 messages
for each domain:result combination. When the server is queried during
the SMTP envelope phase (MAIL FROM), it also queries any configured
peers, and the scores are combined. Domains with a history of spam for
a given SPF result are rejected at MAIL FROM. The GOSSiP system has
a command line utility to reset (delete) a reputation for cases where a
sender that was infected with malware is repaired. In addition,
the confidence score of a reputation decays with time, so a bad sender
will eventually be able to try again without manual intervention.
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