[Mimedefang] Mimedefang/Multiplexor wrong score. Stops running tests randomly

Stephen Johnson (DIS) Stephen.Johnson at arkansas.gov
Fri Jul 18 10:54:26 EDT 2014

On Thu, 2014-07-17 at 18:51 -0400, Justin Edmands wrote:
> Hey,
> Mimedefang is not appending the appropriate score to our messages.
> An example would be a message manually run through spamassassin
> produces a 17.6 score. This same message processed by the mimedefang
> filter only produces a 0.698. This is all run on the same server. What
> the heck? It only runs those tests? It runs random tests sometimes. I
> have no idea why. Does it have a max process time or something causing
> it to stop running tests after X time? Anyways...

You are misunderstanding how Mimedefang uses spamassassin.
Spamassassins's rewriting of e-mail headers is done when it's used after
the MTA has accepted delivery of the e-mail. Mimedefang runs as a milter
(mail filter) within sendmail itself. That means that an incoming e-mail
is still in the processing of being received when Mimedefang get's
called be sendmail. The e-mail can't be rewritten by spamassassin. 

The only way to modify the incoming e-mails is via milter API calls. And
only Mimedefang itself has to do the rewrites. Spamassassin in this
scenario is only used to run the tests. If you are using the default
Mimedefang filter (/etc/mail/mimedefang-filter), you will see some
rewriting code happening in the fitler_end() function. 

And in terms of how spamassassin works espceically inside run within
Mimedefang. Spamassassin data (e.g. bayes filter database, autowhitelist
database, etc), the data is stored on a per user basis. That means the
spamassassin runs its tests using data stored in the user id that
Mimedefang runs under. Running the same e-mail on a different user it
will result in different test scores. If you want a semi-accurate
spamassasin check of an e-mail as Mimedefang sees it, it has to be done
under the Mimedefang user id.

Stephen L Johnson  <stephen.johnson at arkansas.gov>
Unix Systems Administrator / DNS Hostmaster
Department of Information Systems
State of Arkansas

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