Gmail IMAP periodically fails to work with Thunderbird.
Thunderbird will occasionally stop sending or receiving Gmail for a day or two. But meanwhile, Gmail keeps on working in the Chrome browser, if I load that. Pasted:
Application Basics Name Thunderbird Version 67.0b3 Build ID 20190507203408 Update History Update Channel beta User Agent Mozilla/5.0 (Windows NT 10.0; WOW64; rv:67.0) Gecko/20100101 Thunderbird/67.0 OS Windows_NT 10.0 Profile Folder (Local drive) Build Configuration about:buildconfig Memory Use about:memory Performance about:performance Registered Service Workers about:serviceworkers Launcher Process Disabled forcibly Multiprocess Windows 0/0 Disabled Google Location Service Key Missing Google Safebrowsing Key Missing Mozilla Location Service Key Missing Safe Mode false Profiles about:profiles Mail and News Accounts ID Incoming server Outgoing servers Name Connection security Authentication method Name Connection security Authentication method Default? account1 (imap) imap.gmail.com:993 SSL/TLS Normal password smtp.gmail.com:465 SSL/TLS Normal password true
선택된 해결법
Apparently, Gmail forgot who I was. I discovered a small hidden window. It said that I had to sign in again to Microsoft/Google/Gmail. I did that and then it asked me to give it permission to (again) share with Thunderbird. Problem solved.
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At the top right of the Thunderbird window, click the menu button 
> Options > Account Settings
Then set the 'Authentication method' to 'OAuth2' for both, incoming, and outgoing server of your Gmail account.
You may also need to allow cookies for https://accounts.google.com in Thunderbird.
선택된 해결법
Apparently, Gmail forgot who I was. I discovered a small hidden window. It said that I had to sign in again to Microsoft/Google/Gmail. I did that and then it asked me to give it permission to (again) share with Thunderbird. Problem solved.