The error in title is returned with an NDR for SOME outgoing emails sent through Exchange 2007 to an address with a dot in the username part of the email address. The server doesn't reject the "dotted" addresses all the time. I just sent a test to "firstname.lastname@example.org" and it made it OK. Send to "email@example.com" and it bounces about 1 out of a hundred addresses (the issue is with .gov and .mil recipients). To be clear, it's not that 1/100 sending tries will fail - if the server fails to send to an address it rejects that address all the time.