Your last post got me to thinking, so I did a little further research on the original poster’s IP address. Interestingly enough:
126.96.36.199/19 is listed on the Policy Block List (PBL)
Outbound Email Policy of The Spamhaus Project for this IP range:
This IP range has been identified by Spamhaus as not meeting our policy for IPs which should deliver ‘direct-to-mx’ mail to PBL users.
[color=#CC0000]Important: If you are using any normal email software such as Outlook, Entourage, Thunderbird, Apple Mail, and you are being blocked by this Spamhaus PBL listing when you try to send email, the reason is simply that you need to turn on “SMTP Authentication” in your email software settings (Tools : Accounts : Properties : Outgoing Mail Server : check “My server requires authentication”).
If you do not know how to do this, ask your Internet Service Provider for help with “SMTP Authentication”.[/color]
that from: http://www.spamhaus.org/pbl/query/PBL115295
I think that is probably worth a try!