I'm unsure of what your problem is. First, POP is still available with Oauth. Second, if you have two IMAP accounts for gmail, you need the incoming server and outgoing server defined for each.

All the accounts are existing gmail accounts, so I would think they would all use the same servers.

POP3 accounts don't offer OAUTH2 authentication (for me, at least) which was why (I assume) they quit working on May 28th.

You need separate server definitions for each account.

I don't know what that means. Sorry if I seem thick, but each account has it's own defined servers (although they all are the same). Or they would have, if I could get the "Done" button to get past the error.

It may help to know exactly what servers are already defined and for how many accounts.

I changed from imap.gmail.com to imap.googlemail.com and got past the error, but it now hangs on checking password. I've set it to OAUTH2 and responded "allow" to Google's access request. I've tried the username with and without the @gmail.com suffix and both hang, although with it, Google pre-fills the login page for the access request, so I think including @gmail.com in the username is correct. I've waited 20 minutes for the "Checking Password" phase, so maybe I'll just let it spin for a longer time.

I've also tried "normal password" which responds immediately with "Is the username/password correct?" so I think the OAUTH2 selection is correct. I think I've tried all the various combinations, although canceling out of the wizard results in the "server already exists" error unless I restart Thunderbird.

It may help if you explain what accounts are there. I just took a profile that has a gmail account and created a new gmail account with no problems. I filled in everything except password and let it automatically set up the account. So, there is missing information on what you are doing and what accounts are still on your profile. Yes, keep gmail dot com, not googlemail. Are you trying to manually set up the account? If so, stop and do it again and let TB do it automatically. That seems to be part of the issue.

OK, here is what I'm doing:

1) File/New/Existing Mail Account

2) Filling out as you suggest: [screen1]

3) Yields: [screen2]

4) Adding more info: [screen3] yields same result. Tried with and without @gmail.com in Username field.

5) Changed port from Auto to 993 and account is created. 6) Attempt to check email as is results in password failure. 7) Changing Authentication to OAUTH2 results in request from Google for allowing access. 8) re-checking email results in blue "working" icon (indefinitely, it seems)

I think you need to upgrade TB to a current version. And on the setup, specify SSL/TLS and port 993 for incoming.

My version 38.5 indicates it is up to date.

That release was the last in that series, probably in spring of 2016. The current release is 91.1.0 There have been six major releases since release 38, and roughly 10 to 25 versions released of each.

A list of releases is at https://www.thunderbird.net/en-US/thunderbird/releases/

The latest version seemed to create the account, but the password fails, and if I enable secure authentication (checkbox) it says the server doesn't support it.

Under the newest version, my main email has now stopped working due to

"Application-specific password required: https://support.google.com/accounts/answer/185833"

Remember, Gmail requires specific authentication. Here are the basics:

- change your security authorization to Oauth2 (do this for the incoming server settings and also for the Outgoing (SMTP) server - two places - remove the password entries for the account (remove the entire entries both incoming and outgoing) - that password info is at Tools>Preferences>Privacy&Security - click 'saved passwords' Then click 'show passwords' then highlight the rows with incoming and outgoing gmail servers and click DELete. - check to ensure that TB is set to accept cookies (that setting is just above the Passwords section) - Google will then step you through the authentication process for your PC.

When I try to check my main email, I get a Google login screen, a message on my phone, then it doesn't actually load any emails. If I hit check email again, it goes through the whole sequence again (I have checked stay logged in).

Did you follow the suggested steps?

What authentication method should I use? OAUTH2 doesn't work despite repeating the authorization process each time I try to check mail.

You might think I'm a complete idiot, but I have an advanced engineering degree from a famous Institute of Technology and things are not usually this convoluted when I try to recover from Google being so helpful :-)

I followed your steps and continue to not get anywhere.

I did NOT delete my main account, because I have too many folders and emails that I don't want to risk losing. Unlike in your prior instruction, my incoming server is set to imap.googlemail.com, which is what it was when the primary email was working until the upgrade.