Please explain the problem in detail. What happens? What is the exact error messages?

We're Sorry. We cannot process your request at this time. We apologize for the inconvenience.

That's it. Before this my apple mail was having an intermittent problem where it was not automatically getting the emails from att webmail so I signed in and out of att webmail which was the troubleshooting step att has online, and then I have this problem. My att webmail now downloads automatically to apple mail but I can't log into att webmail with Firefox, which I do to check my spam folder. Only can get in with Safari. ATT says it's an Apple problem with the email client. I haven't called them yet because I think it's an ATT/yahoo problem, which is how it started. The message used to say it was a server problem.

This sounds like a website issue. Contact their support.

Hopefully, I've solved this. The problem may have been I had to sign into yahoo mail in addition to att.net, since yahoo runs the att servers. Right now, everything is working since I did that. Two ATT technical support people did not figure this out but blamed Apple. I thought it was Firefox since there was no problem when I used Safari. Apparently, something with Yahoo is amiss. It seems to be another symptom of the ATT/Yahoo mail setup, where ATT doesn't use its own servers for its webmail. This should never have happened. ATT if you're listening, the process of using email should be seamless and invisible to the customer even if you don't control your own system by using Yahoo. It's not. It's always been confusing and awkward and really, this should never have been.

That was very good work. Well done. Please flag your last post as Solved Problem so others will know.

I believe it is solved.