This is a new install (2 seeks old) of Exchange 2003 on Windows 2003 (member server in a Win2003 domain). We moved from a hosted solution to our own exchange server. When users were setup in AD, they were created with the domain names and email addresses to match (same as thehosted addresses) As part of the migration, we created new email addresses for everyone (added a . between their names) and made that the new default email address for everybody. The problem is when people send to the new addresses, sometime they go through, sometimes they are bounced back with the messages below. The old addresses (which are not the exchange default addresses) work fine every time. When the problem exists, if I go to DNSSTUFF.com and do the email test, the old address is fine, the new address reports the same 550 error seen below. Anyone have any ideas????? Recipient address:myuser@mydomain.com Reason: Remote SMTP server has rejected address Diagnostic code: smtp;550 Requested action not taken: mailbox unavailable Remote system: dns;mail.mydomain.com (TCP|100.100.4.196|65323|200.200.218.66|25) (SMTP service ready) Reporting-MTA: dns;mta1.srv.hcvlny.cv.net (tcp-daemon) Original-recipient: rfc822;myuser@mydomain.com Final-recipient: rfc822;mysuer@mydomain.com Action: failed Status: 5.0.0 (Remote SMTP server has rejected address) Remote-MTA: dns;mail.mydomain.com (TCP|100.1006.4.196|65323|200.200.218.66|25) (SMTP service ready) Diagnostic-code: smtp;550 Requested action not taken: mailbox unavailable

hi might wanna look at this article http://support.microsoft.com/?id=828263 let me know if it was helpful

I already have the firewall set to allow UDP packets up to 1200 bytes. However, I do think the issue is firewall-related. I am pursuing that angle. Thanks!