Could you add a screenshot from the error console (press in the same time these 3 buttons on your keyboard when you are in Thunderbird: Ctrl-Shift-J) to see if there is something about Gmail connection? On that Thunderbird profile you have only gmail or also other accounts (from other service provider) - if you have also others - the rest of them work? Also, what TB version do you have?

I don't think it's an internal error in Tbird but rather that Gmail sees the attempt to connect as "insecure", I get their email saying that, but then there's no way to fix it that I can find. Here's a snap. hope your eyes are better than mine.

oh p.s. Gmail is the only account in my TB, set up as IMAP, working great for years until this Windscribe usurpage.

I don't see anything strange in error console - do you have an anti-virus software? If yes try to exit or stop the protection for a wile and test if that change something (please note that some anti-virus software do not stop all services so you might need to set it of till you manually start it and also a restart on your computer). While the anti-virus is off I recommend you to not access other software and/or some internet pages...

Tried it with no antivirus processes running, still rejects login.

You might post here your Thunderbird Troubleshooting information, then we might can see if you are using the correct settings: At the top right of the Thunderbird window, click the menu button (or use the regular menu at the top), then select Help: Troubleshooting Information. Click the "Copy text to clipboard" button. Do not check the box "Include account names" Then paste (Ctrl-V), the text into your response here. We only need to see the sections down to and including the "Extensions" section, so you can delete the rest.

Since nothing has changed or been added to TB since it was working perfect with Gmail, I think the focus needs to be how to:

• a. somehow bypass Gmail's security check that's blocked TB since Windscribe took over my net access, or
• b. get rid of the Windscribe factor (it's already been thoroughly uninstalled with Revo)

Can you access Gmail with TB when you're under a VPN?

Focusing on the internals of TB seems like a waste of effort. But here:

  Name: Thunderbird
   Version: 78.2.2
   Build ID: 20200908210243
   Distribution ID:

   Update Channel: release
   User Agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.2.2
   OS: Windows_NT 6.1

   Launcher Process: Enabled
   Multiprocess Windows: 0/0
             Disabled
   Remote Processes: 0
   Enterprise Policies: Inactive
   Google Location Service Key: Missing
   Google Safebrowsing Key: Missing
   Mozilla Location Service Key: Missing
   Safe Mode: false

 Mail and News Accounts
   account3:
     INCOMING: account3, , (none) Local Folders, plain, passwordCleartext

   account4:
     INCOMING: account4, , (imap) imap.googlemail.com:993, SSL, passwordCleartext
     OUTGOING: , smtp.googlemail.com:465, SSL, passwordCleartext, true
     OUTGOING: , smtp.googlemail.com:465, SSL, passwordCleartext, false

 Crash Reports for the Last 3 Days

 Remote Processes

   Type: Count

 Extensions

     Name
     Version
     Enabled
     ID

       Amazon.com
       1.1
       true
       amazondotcom@search.mozilla.org

       Bing
       1.0
       true
       bing@search.mozilla.org

       DuckDuckGo
       1.0
       true
       ddg@search.mozilla.org

       Google
       1.0
       true
       google@search.mozilla.org

       Grammar Checker
       0.9
       true
       grammarchecker@codedgers.com

       Mail Merge
       7.2.1
       true
       mailmerge@example.net

       Open With
       6.9.2
       true
       openwith@darktrojan.net

       Remove Duplicate Messages
       0.5rc1
       true
       {a300a000-5e21-4ee0-a115-9ec8f4eaa92b}

       Search Results Sort By Date Not Relevance
       1.18
       true
       srsbdnr-@ntispam-caseyconnor.org

       Wikipedia (en)
       1.0
       true
       wikipedia@search.mozilla.org

       AttachmentExtractor
       1.3.5.1
       false
       {35834d20-efdb-4f78-ab77-9635fb4e56c4}

       Extra Format Buttons
       1.3
       false
       extra.format.buttons@codefisher.org

       Gather the Senders !
       1.2.2
       false
       gatherauthors@fabien-tools.net

       Mail Redirect
       0.10.9
       false
       {CC3C233D-6668-41bc-AAEB-F3A1D1D594F5}

       Quick Folder Move
       1.8.2
       false
       quickmove@mozilla.kewis.ch

       quickFilters
       4.4.1
       false
       quickFilters@axelg.com

       QuickFolders
       4.18.1
       false
       quickfolders@curious.be

       SortPref
       1.1.4
       false
       {bfa92939-6ded-4a3f-885f-55dfcce728b8}

       Theme Font & Size Changer
       56.0
       false
       {f69e22c7-bc50-414a-9269-0f5c344cd94c}

       Theme Font & Size Changer for Thunderbird
       64.6
       false
       tbthemefixed@wanhunglo.com

       ThunderBrowse
       3.82
       false
       ThunderBrowse@thunderbrowse.com

 Security Software

   Type: Name

     Antivirus:
     Antispyware:
     Firewall:

I have just received from another user a message that with a VPN connection, setting security "ssl/tsl" and authentication method "OAuth2" did the trick. Can you try like this? If doesn't work from the start you might try also to enable Cookies in TB Options/Privacy for OAuth2

Did you mean by "with a VPN connection, setting security "ssl/tsl" and authentication method "OAuth2" did the trick." that these settings are in TB itself?

Yes - on TB, for that (those) accounts. Connection security - SSL/TSL, authentication OAuth2

It's fixed, for now. Somehow Gmail had decided that TB was in the "less secure" zone and I had to turn on less secure access for TB. https://support.google.com/accounts/answer/6010255?hl=en

Just want to thanks SVlad2009 for all the help!

BTW, when I spoke with Xfinity/Comcast tech to try to fix this, the guy couldn't believe I was calling about problems with the "OBSOLETE THUNDERBIRD EMAIL" client. =8-b

V8? For real? Or it's a typo?

=8-b is a sideways horizontal ascii emoji showing a human with surprised hair, glasses, a nose, and a mouth with tongue out

)))) Ok, got it! :)