We're getting the following error when mailing a particular email address
User<firstname.lastname@example.org> - (501 #5.1.1 bad address email@example.com)
The address is valid as i can mail from Hotmail but no one can mail this address from our company.
We definitely have the right address (no typos) and all other external mail (from our company) is fine.
We're running Exchange 2003 and MailMarshal.