well maybe I should study the relevant RFCs before making suggestions :-) Sorry for that.

Well, one thing I could think of is to build in some extra "intelligence" into
courier. 1. Never accept outgoing mail with bad headers. 2. Accept local mail with bad headers, but add a notification to the e-mail that
it is corrupted. Maybe there could be introduced a switch how to handel local
corrupted mail: 1. attach as plaintext (the existing implementation), 2. attach
a notification to the original mail but keep it a Mime formatted mail (This will
lead into troubles, too, but is not as worse as turning off the checks
completely).

As I mentioned in an earlier mail I tried to build a new Mime message around the
corrupted message. The result was an at-the-first-glance-correct Mime message
saying "corrupted message". The original mail could be read via pop3 but not via
imap. Imap didn't show the message body. My suggestion of using message/rfc822
is indeed just moving the problem from the mta to the delivery agents and
clients - but not solving it.

Regards Manfred