Unable to Send Mail OSX10.6.8

Hi,

Suddenly I'm unable to Send messages in Mail from any of my email addresses ...they just immediately go to the Outbox & sit there.

Have made no changes in Accounts Prefs settings prior to the issue.

Have double checked all info, passwords, etc.

Have since tried all sorts of changes, including AT&T's automated email setup app, live Chat via AT&T support...things have actually gotten worse, now I also don't Receive messages either.

No issues with Web...can access via Web mail & iPhone, but not home computer.

Driving me nutz...!

Any & all help is greatly appreciated.

Best Regards, SS

Mac Mini mid-2010

OSX 10.6.8

Mac Mail 4.6

AT&T U-Verse lower southeastern MI