malformed MIME headers are dropped

[ilpadrino]

My SMTP gateway drops some emails due to malformed MIME headers. Usually these dropped messages include an attachment. The message is dropped as a precaution becaused of malformed MIME headers and the attachment cannot be scanned for virus.

Does anyone know what causes malformed MIME headers? Is it the sender's email client or server and how can we help senders fix the problem?

Thanks.