Nix that last note. I found it. It was already set to:
1) Server type : IMAP Mail Server
2) Server Name: imap.gmail.com
3) User Name: correct name and address
4) Security Settings:
Connection security: SSL/TLS
Authentication method: OAuth2
Torbirdy with Enigmail
I solved the problem: all settings were correct, torbirdy connects with the TBB successfully, the connection was refused by the Gmail server because, per "Security in a Box" https://securityinabox.org/ru/thunderbird_torbirdy
I**t is worth noting that some email providers such as Google Mail may refuse a connection to the email server via the Tor network.**
Plus, torbirdy corrupted Thunderbird and the problem required a clean installation. It now works with Enigmail and I've ditched torbirdy. Easier to use Sigaint or GPG with Apple Mail or Enigmail with Thunderbird.
I'm glad it works now. If you still want to use Torbirdy sometime in the future, you might consider trying a Riseup email account, which plays nicely with Tor. I use Gmail for various things, but I long ago gave up trying to use it with Tor. Riseup has its own downsides, however, most notably that it doesn't support two-factor authentication.
The value Torbirdy provides is that it hides your location from your mail provider and from a passive network adversary. The problem is that, if you're like most people, you have a dozen+ different applications pinging a home server all the time, plus a cell phone, probably, so in order to take advantage of Torbirdy, you would need to route that other traffic through separate Tor circuits, and then compartment the stuff you can't Torify by not using those connections at the same times or locations as your Tor connections. Unfortunately, none of this makes much sense unless you have a specific adversary (like a stalker, an ex-partner who works for a telco, your example here) with specific capabilities. Otherwise, you're just kinda driving yourself nuts with an impractical setup, that is, unless you're not bothered by using Tails, Subgraph, or Whonix as a daily driver, without a cell phone, in which case godspeed and I salute you, I guess.
Glad to hear that Thunderbird & Enigmail is working for you though. Apple Mail has a much better UX... I personally prefer Mutt or herpes to Thunderbird.
I can send you two Riseup invites if you want them. Gmail is next to impossible to use with Tor. If they made 2fa mandatory, then their security team wouldn't have to rely on blocking connections from "suspicious" IP addresses, but a ton of users would balk at being forced to use 2fa, so Google hasn't done so.