<i>locked as duplicate of [/questions/1496958] in Thunderbird section even though this thread could have been moved</i> I checked the settings multiple times. The settings you see in the screenshot are correct. These are the settings I've used for the past 10 years. No problems until now. I just logged in today and Thunderbird did not want to work. K-9 Mail works just fine on all my Android devices. This is happening only on Thunderbird desktop. • To troubleshoot the problem, I first removed the account and added it back. That did not work. • Next, I uninstalled Thunderbird and installed it back. Same problem persists. • This time I uninstalled Thunderbird using Geek Uninstaller to remove all related cache. Install Thunderbird back and try again. Did not work. • Read A2Hosting article a bunch of times: https://www.a2hosting.com/kb/getting-started-guide/setting-up-e-mail/accessing-e-mail-accounts-with-client-applications. Confirmed, all my settings are correct. Thunderbird is still not working.