Sending of password for user jimxxxx@bellsouth.net did not succeed. Mail server inbound.att.net res

I'm unable to access my Bellsouth.net email account using Thunderbird on my desk top. I get the following when trying to log in:
Sending of password for user*****@bellsouth.net did not succeed. Mail server inbound.att.net responded: Server error - Please try again later.

It has worked for years, but this weekend I continually get the above error message. I have checked my password by using AT&T's web mail successfully. Interestingly my iPad and MacBook Pro, both of which have worked fine to access my email are unable to retrieve my email. I have checked my account settings against AT&T' recommendations and nothing has changed. I've got to assume that something has changed on AT&T's end.  Can anyone help me out?

Thanks in advance,

Jim

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