After Upgrading from 5.5 to Exchange 2003 SP2, POP3 clients can no longer send email to external accounts. They can send to email accounts that are internal (my email server does not have to forward/relay email out to another email server).
MAPI clients can send to external accounts.
I get the following error message when POP3 clients try to use my mail server to forward (SMTP) email to external accounts:
The message could not be sent because one of the recipients was rejected by the server. The rejected e-mail address was 'firstname.lastname@example.org'. Subject 's', Account: 'pop3.hanman.com', Server: 'smtp.hanman.com', Protocol: SMTP, Server Response: '550 5.7.1 Unable to relay for email@example.com', Port: 25, Secure(SSL): No, Server Error: 550, Error Number: 0x800CCC79
Is there some reason why OL2003 does not work, but 5.5. did work?
Is there a simple setting on the OL2003 Exchange server that I need to change?
The OL2003 Exchange Server has to forward email out to the Internet through a Pix 515 firewall running 6.3.4 code; could this be the issue?