Rejected responses from users that exist

I’m running RT 3.0.4 on FreeBSD using MySQL, mod_perl1, and Postfix as MTA.

I have 1 user that is able to send an email into the system, triggering his
user creation, and the ticket to be opened. He receives a response w/ the
ticket number info.

If the then tries to update the ticket via email, I get a “could not load a
valid user”.

This only happens to him and only on 1 of his email accounts.

He is running Outlook 2000 and Exchange Server 5.5.

I think there must be something about the way Exchange 5.5 is crafting the
message that causes RT to mis-parse it.

I have a buddy testing Exchange 2003 Beta and that works fine, so its either
a bug from 5.5 that’s ‘fixed’ or its this users particular configuration.

Any ideas? I’ve looked at the mail logs and the “from” is crafted the same
way every time.

I posted about this before (running 3.0.2) and didn’t get any responses. Has
no other person had this problem? I know Exchange 5.5 is pretty old, but
many companies still use it.

Is there anything in particular that would help in debugging? Version
numbers of anything RT uses? Log line clips?