501 Badly structured mime attachment

Incoming mail :
Some of our customers send us mail with attachments and end up with receiving a NDR :
501 Badly structured mime attachment. The recipient does not get anything. I checked the Tech Q&A, found similar problems, but not quite what i am looking for. It must have something to do with the mail program of the sender, mime and uuecode and double in the header. But can i adjust my Exchange server for this ?

Thanks