This worked on 3 workstations that stopped working on the same day. This could also apply to other services, but ATT POP3 Email it did work with these specs:
Windows 7 x64 Pro with Office 2007 Sp3 Pro
If you know your settings are correct by the newer email settings, which you can check here at ATT's website. http://www.att.com/esupport/article.jsp?sid=KB401573#fbid=Gvsy_vR5KOw
If you did the settings correctly it should give you no errors sending and receiving dialog box. But the email is still picking its nose in outbound.
Easiest way to check is to put outlook into safe mode and send an email. If it sends, no more calling ATT support. I’m pretty sure it will work.
Hold down Ctrl key and double left click on outlook icon to put outlook into safe mode.
In Outlook 2007 SP3 go to Tools menu dropdown and drill down to Trust center.
Find and click Add-Ins
You should see all active and non-active add-ins. It could be any of the add-ins listed with a check mark, and it’s a trial an error process. It’s pretty quick though.
Try unchecking the SharePoint add-in first and then close outlook and launch normally.
I got lucky and the email sent without issues and still working.
(If this worked for yah lmk , so it helps others with the same issue. Thx)