Postfix being an ass: Relay access denied when rcpt to: is issued

[Archangel]

Ok, Postfix is acting like a three year old.
When I try to send e-mail in roudcube, it returns, "Relay access denied".
I telnet to port 25 on the server, ehlo and rcpt from without a problem.
When I enter mail to: u...@domain.com it returns 554 5.7.1 <u...@domain.com>:
Relay access denied.  Apparently, this is a postfix issue, but idk how to
fix it...even reinstalling postfix from scratch doesn't fix it.  Help.
-Aaron