Logged In: YES 
user_id=12800

When I run the referenced message (well, the subpart with
the broken header) through current Python2.3cvs's Parser, I
get a message where the line "content_id=xmailer_a0" is the
first line of the body.

We changed Parser so that in lax mode, the first non-header
like line (not necessarily a blank line) stops the header
parsing.   Since this seems as reasonable as anything else
in this case, I'm closing this bug report.