One other reason for the request is that I suspect a bug, or at least an incompatibility with signed+encrypted messages that get incorrectly transformed into a message with a single attachment called smime.p7m which the webmail >cannot identify. This occurs every time I receive a signed+encrypted email generated at the external sender from outlook through ciphermail and have cipermail decrypt the message (my server is set to not remove signature from >messages - again I want users to have a maximum visibility of what happens to their communications). This was raised previously to this list (july 21st) but I could not see a final answer.
we had a similiar problem with the smime.p7m attachement and Martijn solved it for us:
For the record, since it might help someone else having a similar
problem, it turned out that the message was correctly decrypted however,
the resulting message was opaquely signed. An opaquely signed message
can only be read with an S/MIME aware application (a clear signed
message can be read like a normal email). Since the mail application
that had to extract the attachment was not capable of reading S/MIME
opaque signed email, it did not detect the attachment. The solution was
to have the gateway remove the digital signature by checking the
advanced S/MIME setting "Remove signature". The will remove the S/MIME
signature which then results in a normal email with the attachment.