Be sure you have Oauth2 set for security. Then, be sure to remove all passwords from account. Then connect and Google will prompt you through to authenticate. Your old password works online, but not on any email client (not just TB).

Thank you, David. Progress made, but the problem remains:

OAuth2 was and remains set for security.

I removed all passwords from my account via Preferences/Passwords/Remove All

A Google window opened, prompting me through to authentication, which I did.

I followed the links in new Security Alert emails from Google and confirmed it was me.

Thunderbird Preferences/Passwords/Show Passwords now reveals only a Google-generated password/link beginning 1//0d

I did a test, then a restart, then another test. Gmail still downloads new emails to Thunderbird, but when I try to send an email from Thunderbird it continues giving me the same messages:

"Login to server smtp.googlemail.com with username p****.*****ss@gmail.com failed."

And: "Sending of the message failed. Unable to authenticate to Outgoing server (SMTP) smtp.googlemail.com. Please check the password and verify the 'Authentication method' in 'Account Settings | Outgoing server (SMTP)'."

Troubleshooting information (below) seems largely the same. Any ideas?

Thanks, Percy

Application Basics Name Thunderbird Version 91.10.0 Build ID 20220525135609 Distribution ID Update Folder C:\ProgramData\Mozilla\updates\8216C80C92C4E828 Update History Update Channel release User Agent Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101 Thunderbird/91.10.0 OS Windows_NT 10.0 19043 Application Binary C:\Program Files (x86)\Mozilla Thunderbird\thunderbird.exe Profile Folder (Local drive) Build Configuration about:buildconfig Memory Use about:memory Performance about:performance Registered Service Workers about:serviceworkers Third-party Modules about:third-party Launcher Process Enabled Multiprocess Windows 0/0 Fission Windows 0/0 Disabled by default Remote Processes 4 Enterprise Policies Inactive Google Location Service Key Missing Google Safebrowsing Key Missing Mozilla Location Service Key Missing Safe Mode false Profiles about:profiles Telemetry Data about:telemetry

Well, I'm no expert; there are a few real gurus here, but I'm not that skilled. from what you describe, I suggest going to accountsetting>Outgoingserver and check that your smtp server is set to Oauth2. And maybe recheck your smtp password to ensure it was removed.

Brilliant! Problem solved! The key was finding the Outgoing Server setting, which was hidden out of site in my Account Settings below several other accounts. When I scrolled down and clicked, I saw that all outgoing mail was still set on normal password. Changing to OAuth2 fixed everything. Thanks!

I was glad to assist. Please mark this completed so it will be removed from active list Thanks much.