As of the last beta update, 135.0b2, I cannot access my AT&T email account. Gmail still downloads.
As stated above, as of Jan 13th, the date of the last update, I can no longer download any email from the Yahoo/AT&T server. My Gmail email downloads like before the update. Did anything change to influence my AT&T account? I have no issues with accessing the email online, or my phone, so the AT&T email account still works the same everywhere but in Thunderbird.
Alla svar (2)
why are you using a beta, when it appears that you want reliability? I suggest you consider switching to a release version.
Try removing the entry for the account in Saved Passwords in Settings, restart TB, and enter a new secure mail key (created on the AT&T site) when asked for a password. AT&T apparently also supports OAuth2 authentication, but I believe it isn't yet supported in TB for AT&T (it is for gmail, outlook.com, Yahoo, AOL and a few others).