An added info just so you'll know.
I was finally affected by this change on May 1 2012.
The ATT website said this...
"but if you are using the old server settings (pop.att.yahoo.com and smtp.att.yahoo.com), they will continue to work. You do not have to change them at this time."
Mine was through yahoo and that old setting delayed my e-mails over 12 hour
Made the change to the new setting and it's working normal so far