SMTP relay for LG Rumor

Hey, all! I've got an Sprint LG Rumor that I'm trying to configure to use with my Mac OS X 10.4 Server's email via IMAP. I can connect to my IMAP account just fine. However, sending email has become an issue. Sprint's smtp server requires smtp auth, which is not possible on the LG Rumor (it tries to pass the same credentials as what it passes to the IMAP server). So I figure... What if I could enable smtp auth on my Mac Server? The problem I'm having is that it keeps denying the relay, even if I tell my phone to use smtp auth. Where do I even begin?