Mark Sapiro replied to one of my postings:

Mailman (actually the Python email package) doesn,t like the fact that there is no intervening empty line between the terminating boundary of the message/rfc822 part and the terminating boundary of the outer message.

Quoting from section 5.1.1 of RFC 2045

The boundary may be followed by zero or more characters of linear whitespace. It is then terminated by either another CRLF and the header fields for the next part, or by two CRLFs, in which case there are no header fields for the next part.

For the record (i.e., anyone who looks in the archives), the RFC is 2046. This DSN message is being generated by our Ironport anti-spam appliance, so we will report this to Ironport.

Barry S. Finkel Computing and Information Systems Division Argonne National Laboratory Phone: +1 (630) 252-7277 9700 South Cass Avenue Facsimile:+1 (630) 252-4601 Building 222, Room D209 Internet: BSFinkel@anl.gov Argonne, IL 60439-4828 IBMMAIL: I1004994