had this problem and I had to just play with the setting on the smtp to get it working. Then I had problems with the mail I sent getting marked as junk by msn, yahoo,.....

Oh. Be sure to use the Allow in this list. I tried the other way and bots on the outside found my server and used it to relay porn to mask where it was coming from. I was sending 1000 of porn a sec. I only knew because of my virus scanner;it got locked up.

I have the doman I am using in the from field in my allow list.