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Re: Virus emails

On Tue, Sep 23, 2003 at 08:39:02AM -0400, H. S. Teoh wrote:
> > > What are the exim rules you used to catch these things?
> > 
> >     exiscan-acl calling clamav and dropping it with a 550.  A full log
> > line would be:
> > 
> > 2003-09-22 07:38:05 1A1RpB-0007Xd-Of H=(smtp21.singnet.com.sg)
> > [] F=<josen@mbox3.singnet.com.sg> rejected after DATA: This
> > message contains a viru s or other malware (Worm.Gibe.F).
> I see. Thanks for the info, I'll look it up.

exim4-daemon-heavy includes the Exiscan patch that allows one to scan for
malformed MIME, viruses and spam during the SMTP dialogue.

Install clamav-daemon and in the general settings block add:

av_scanner = clamd:/var/run/clamd.ctl

And in the ACL block after DATA, you put something like:

  deny message = Message contains malware ($malware_name)
       demime = *
       malware = *

Works wonders.

There are also similar low-level interfaces to SpamAssassin: one is via a
sa-exim.so that is loaded via the local_scan() interface,

local_scan_path = .../somewhere/sa-exim-3.0.so

And another one is via an exiscan ACL setting for it (also in the DATA ACL),

  deny message = Classified as spam (score $spam_score)
       condition = ${if <{$message_size}{80k}{1}{0}}
       condition = ${if <{$spam_score_int}{120}{1}{0}}
       spam = nobody

(that 120 is 12.0 in SA terms)

For now I'm using the SA-Exim method because even though it's clumsy (needs
the .so file compiled from source so distribution isn't as trivial as an
apt-get invocation), I used it before the Exiscan patch was available and it
was reliable. (I'd welcome suggestions from other users about this issue.)

> > > If you want to automate this more, you could write a spamassassin rule
> > > that matches Swen mails, then use procmail to filter it (match against the
> > > rule name in X-Spam-Status) through a script that grabs the IP address and
> > > enters it into the firewall.
> > 
> >     Except it never hits SA nor do I even have procmail installed.  Can't
> > stand the ugly beast.
> It never hits SA?

Because his antivirus ACL kills it before that.

     2. That which causes joy or happiness.

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