Thunderbird suddenly stopped receiving AT&T email

The other day Thunderbird stopped receiving email on my AT&T email addresses. I have several & they worked but later on they did not. They can still send email.

New email does show up on the att/yahoo server so it is getting through to that point.

I have a gmail address which still can receive email with Thunderbird.

I logged on to the att.yahoo.com email server & deleted the Secure Mail Key and created a new one & entered this into TB. Did this on one of the addresses but it made no difference.

When opening TB for any of the AT&T addresses, at the bottom of the screen it displays the address & “Connected to inbound.att .net”. That would seem to indicate it is connected, however email isn’t getting through. That said, even if I delete the TB inbound password/secure mail key it still says “Connected to inbound.att .net”. That message is always there from the instant TB is opened. It never says sending or opening.

And suggestions on to get AT&T email working with Thunderbird again?
Thanks.

I'd start by asking in the Mozilla support forums.

I read a certificate was revoked.