Question : Exchange 2003 cannot receive email but can send.  OWA also does not work.

Running Exchange 2003 SP2 on Windows Server 2003 SP2.  Can send and receive email  internally within network.  Can send email outside network, but cannot receive email from outside network.  Was working yesterday.  OWA has not worked since IP address migration last week, getting Error 500 after login.  Have been changing settings for Default SMTP Virtual Sever and Default Web Server to troubleshoot OWA issue.  Using FBA and SSL to access OWA.  I think my many tweeks have affected our incoming mail from the outside.  Any suggestions for fixing our incoming mail and OWA issues?  

Answer : Exchange 2003 cannot receive email but can send.  OWA also does not work.

It sounds like a problem with the Default SMTP Server.  Can you tell us what error message a sender gets when they try to email you from the outside?  (Might have to send an inbound message and see what "undeliverable" error, if any, you get in return.)  Make sure the Default SMTP Server allows anonymous authentication, set to port 25, no IP address restrictions for starters.