Digital signature invalidated

[Ben Tullis]

I have been using Mailscanner for about six months quite successfully.
However, I mam having trouble using it with signed e-mail.

Several times a message has been reported to have been changed during
transmission, thereby invalidating the digital signature.

I have tried switching off 'sign clean messages' and 'scan all messages' to
no avail. Not all signed messages are corrupted, but particularly the ones
with a MIME payload such as video/mpeg.

Please help.  I need to implement a company-wide PKI and do not wish to
have to abandon mailscanner.

The virus scanning engine is sophos
Spam asassin is not enabled or installed
Spam tagging is disabled
MTA is sendmail
Server is Debian Linux 2.2

I have not disabled the 'X-Mailscanner: found to be clean' header, but it
was my understanding that this should not invalidate the message body
signature.

Many thanks.

Ben Tullis