Just fyi, some info about what that code means:

https://forums.att.com/conversations/att-mail-login-security/help-with-care-code-2052-lu003/5eebfd6a6880ca6501d96b38

I'd suggest trying to access your mail via a different path. E.g. if you're using a mail reading program, try
logging in with a web browser and read it there. Or if you normally use a browser, try reading it with a
mail program on your phone or computer.

Fyi my mother has an SBCGlobal account that was working fine with Mail.app on an old Mac. But then
they recently changed the servers and she can now only access it from her (new) iPhone or from the
web server. I wasn't able to get the old Mail.app program on her ancient iMac to work.