I spoke with ATT and they provided smtp.att.yahoo.com and suggested changing
the outgoing port to 465. This did not fix the problem
Thank you for that clarification. There are actually three AT&T DSL
services, and you really should specify which of them you have (yeah, I
know, most won't know of the two others than the one they have).
For at&t Yahoo! HSI (which is your version) the help link posted by Kevin
Young has most of the information you need. Additionally, you need to check
here:
http://helpme.att.net/article.php?item=2035
Note that you must use your full email address, and check the "My outgoing
server (SMTP) requires authentication" box.
One of the versions of Outlook (I don't recall if it is 2003, or another
year) has a bug in the SSL routine, and requires the latest Service Pack to
function properly.