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

[DeathTorrent]

Ok, Postfix is being a homo.
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: user@domain.com it returns 554 5.7.1 <user@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.

[ABerglund]

I assume that RC and postfix are running on separate servers. If so, you need to tell postfix that it's OK to accept mail from your RC box. Look for the "mynetworks" params in postfix's main.cf.