Exchange user can not send external mail

I have user, just this user, no one else. That can not send external mail, internal is fine, but external is not. I have deleted and recreated his mail, but I have a feeling that it has more to do with the setup of this Exchange server and or his account (he is POPing his mail). I inherited this Exchange server (Exchange 5.5 SP4) I have been on 2000 for awhile now so I am a tad rusty and out of place. I figure maybe it is a relay issue, but the user just receives a non-deliverable mail back. Something to the tune of ?This is recipient was not reachable?. In any case I can?t find the settings for realying. omg I feel like a noob please help.

*posted in multiple forums*