Former TB donor here: My Thunderbird v 91.6.1 has been working nicely for 10+ years. Although I've had the (send/receive) log-in error before I was always able to fix it. I just started getting the dreaded "Login to server...failed." I've followed and repeatedly tried the various tips with no luck. The 3 domain email addresses we use for our websites work. It's the gmail and our Internet service provider's email address (Spectrum-mobile.charter.net) that won't work with POP3 or IMAP. Spectrum support, said it's TB, that they have the same log-in problem with other subscribers. In desperation, I've tried Mailbird and Outlook, both automatically configure all 10 of our email addresses; however, using either application is too different for me. We're a 501(c)(3) educational org and can't afford the Mailbird fees. This 84-yr-old disabled veteran's mind is fading, instructions are hard to follow anymore, so—ideally, I'd like someone to configure our TB remotely so as to get it to work as it was. We have three domains, each with 2 addresses, Kerry@...org, admin@...org, and 1 gmail and 1 Spectrum address. With aloha, Kerry P.S. I back up TB's profile with Moz Backup v 1.5.1 often but it won't “Restore” the profile; I think it's because the back-up was made with an earlier version of TB.