Yesterday afternoon I lost all ability to send emails, although I am still receiving fine. Here's what I've tried so far...

I have tried bypassing Mac Mail and sending directly from my eMail host (Cox).

I have tried changing the outgoing port to 587... and 465... and 2525.

I have confirmed I do not have a virus or trojan (including Flashback).

I have repaired my Permissions.

I have resent my cable modem and rebooted (several times).

Cox has verified my account is not being blocked, and they can send successfully via my account.

I can switch my cable modem to my laptop and send successfully.

What ever this is, it's specific to my Mac Pro (OS 10.6.8) and both Cox and my local Mac Genius's are stumped.

Any suggestions?