I have often these messages in the log:

sogod[1182622:1263604] MimeType 'text/' does not support a parameter named 'type' with value 'multipart/alternative'
sogod[1182622:1263604] MimeType 'text/' does not support a parameter named 'boundary' with value '_0047eb61e13b1a148d9b249c350588e0b7cictex01ictbbch'

From my understanding of MIME these two parameter are actually valid. It looks to me like a false message. Maybe you have to inform the upstream library about it. It could be a parsing mistake as well.

As a sidenote: It would help if you would write out which email is causing this error. If you would print out the ID of the email then it would already help. Thanks. In this specific case I can search now through all emails with the boundary value but this is not always possible. E.g if only the first message would appear then I could only search for "multipart" which would give me 10 million results.