By brother had an issue with outgoing email when he moved to a friends home with att.net. I read and read etc. I found a blog on the att.net utalk website. Funny, I was just going to give up and wouldn’t you know the last post by Scooter and he said:
Port 25 blocking is very common due to spam issues. If you are setting up Outlook to send email via another domain, try using port 587 for SMTP outgoing; this is supported by most ISP’s. (using port 587 does not require SSL)
http://utalk.att.com/utalk/board/message?board.id=HSIA&thread.id=2162&view=by_date_ascending&page=5