I'm not certain whether this is an Exchange or an Outlook issue. It depends whether Outlook transmits messages to Exchange in Internet-ready MIME format, or in some internal format; whichever program is generating the MIME headers in the messages, is generating
them incorrectly.
We have encountered a bug where the References header is, under specific circumstances, being set in a way that violates the standards.
RFC5322 Appendix B states, "Folding continuation lines cannot contain only white space."
The problem we're seeing is that messages are being given a References line which contains:
References: <one message reference>
(some white space)
That's it.
Basically a new, folded header line is being started, but it is not being populated by additional message reference lines. This constitutes a folding continuation line with only white space, which RFC5322 prohibits.
I can reproduce this by taking a specific message and re-sending it to my address. The client is Outlook 2010 SP1, and the mail system is Exchange 2010.
There is no evidence that anyone else has ever seen this issue before, but it appears that no other mail systems enforce this line of the RFC. The affected system goes through a mail relay service which treats this blank folded line as the end of the message headers, corrupting the message, and they are refusing to be liberal in accepting what is, quite honestly, a harmless bug in all other cases.
Regards
Daniel.
