I have clamav scan files once a week, and get the the "LibClamAV Warning: Multipart MIME message contains no boundaries" error, but none of the others.
I've googled the error several times, but have never found an explanation or cure.
A multipart mime message is an email. That it has no boundaries could mean anything. Unfortunately, it doesnt tell me which message might be a problem, so I can't delete it.
Hopefully, I'll find an answer someday...