1. Exchange 2003 New User and New User Mailbox, can send to anyone but can not receive from external senders, can receive internal, all other mailboxes work properly except this new one. Since I did these first two in AD Users and Computers, I deleted the second one also, and then used the SBS Server Management Console to create a new user. Same symptom with new user created in SBS Server Console. All of the other old users have no issues. The bounce back email I get is always the same "Remote host said: 550 5.7.1 No mailbox found [RCPT_TO]"
2. I deleted the user and the mailbox and then created another user with another mailbox. Same exact symptom, once I get this working, a secondary part of this 500 pointer is that I may want to re-attache the original mailbox that I deleted back to the new user.