[exim] MIME parts and sa-learn

Hej,

I am thinking of a clever way to integrate spamassassin's sa-learn
(bayesian classifier training program) into exim's ACLs. The intended
approach is to pass the message which should be trained as a
"message/rfc822" attachment (so original headers are preserved) to a
specific address (e.g. sa-learn-spam@domain) at the server.

Therefore, the first thing I was looking at was the smtp_mime ACL, but
it doesn't seem to be of much use besides filtering for regular
expressions. If the "malware" condition would be allowed, I could pass
the attachment via a "cmdline" scanner to sa-learn, but according to the
docs this isn't possible.

It is of course possible to pass the whole message to a script in the
data ACL or in a transport and demime everything in the script, but I
don't really like that much.
Another approach would be to demime into unique files in the mime ACL
and read these files in a scanner/delivery script, but that's even
worse, IMO.

I'm sure people are using spamassassin a lot out there, so can anyone
here show a smarter way of integration spam/ham learning? (Without using
spamc or sth. else from the user side.)

TIA & br,
daniel