Client staff receiving email with zipped exe file attachments which
are not not detected as spam. Resolved by using procmail to
invoke script "zippedexe".

When zipped attachments are eceived.
Zippedexe uses "ripmime" to unpack the attachments. If the
attachment includes an exe file, an additional header is inserted
into the header which can be used either with SpamAssassin to
increment the spam level appropriately or with a further procmail
recipe to deliver the email directly to a spam folder.

Futher details at http://www.citylinux.com/linux/script/scripts.php?script=zippedexe&man=y