I've been using TB for years with an AT&T account on a Windows 10 desktop. Two days ago all was working well sending and receiving. I stepped away for an hour (without obvious updates or changes) and surprisingly it didn't work, with TB asking for a password but not accepting it. I deleted saved passwords and tried multiple times, even changing my AT&T email password twice. I could access the email account directly through the AT&T website using those passwords. I spoke with an AT&T support rep and he had me delete the account in TB. I did so but now can't reestablish it. I've repeatedly tried to add a new email account using credentials I know are correct, trying numerous POP3 and IMAP protocols, all without success. When TB probes the AT&T servers it says it finds those parameters, but then when it checks the password it fails, simply giving the vague message "Unable to log in at server. Probably wrong configuration, username, or password." I've spent two days researching this problem and trying proposed solutions such as disabling firewalls and anti-virus programs, clearing Windows and internet caches, deleting saved passwords, etc. I was able to set up the account using Outlook on this computer, and if this continues I'll unfortunately be forced to abandon TB and move to Outlook or similar as a substitute. Advice would be appreciated!