I've recently set up an exchange 2003 server and pointed my external DNS records to my external IP. I have checked with my domain service provider and they have confirmed that the settings are correct. From a user account on my internal domain I can send emails to external addresses fine, however when external emails try to send to the email the following error bounces back:
550 550 5.7.1 unable to relay. State 14
Any suggestions anyone? Thanks.