You have 'encrypted password' authentication for the incoming O365 server, but it should be 'normal password', as you have for the outgoing. I don't see a picture of your gmail settings, but the authentication method should be OAuth2 for both the incoming and outgoing servers.

Also, updates to TB 78 from 68 have not been deployed through internal TB updates, so you must have been prompted by an external app or service.

Thanks for that help. My TB isn't there yet, however. I returned the 'encrypted password' for the incoming server to 'normal password' (it had been that way earlier, but I forgot to return it after trying different things). I also fixed the gmail settings to OAuth2 (they've been just 'normal password' for years). Unfortunately, even after shutting down and restarting TB a few times, it is still stuck and neither sending nor receiving on either route.

I haven't tried to rewind to an earlier version of TB. Is that viable?

As for TB asking me to update - it does this every few days even if the current version of TB is up to date. Not sure if that helps diagnose any problem.

thanks again! -Ted

Since you've changed the authentication, try deleting the passwords in Options/Privacy & Security/Passwords/Saved Passwords, check that cookies are allowed in TB Options/Privacy & Security/Web Content (for OAuth2 to work), then restart TB and enter the password when prompted. OAuth2 will prompt with a browser window.

As for the update notifications, check that there is no other app causing this. However, there has been a recent update to TB 78.1.1.

Thanks for your help. I appreciate it. i've done all of that and unfortunately nothing is working. When I get a chance I'll try to revert to an earlier TB.

Thanks for your help. I appreciate it. i've done all of that and unfortunately nothing is working. When I get a chance I'll try to revert to an earlier TB.

That is perhaps the worst thing you can do. At the very least you will loose your contacts. That is if you can jump through all the technical hurdles that have been put in place to prevent data loss through doing that.

Have you tried

• Restart Thunderbird with add-ons disabled (Thunderbird Safe Mode). On the Help menu, click on "Restart with Add-ons Disabled". If Thunderbird works like normal, there is an Add-on or Theme interfering with normal operations. You will need to re-enable add-ons one at a time until you locate the offender.
• Restart the operating system in safe mode with Networking. This loads only the very basics needed to start your computer while enabling an Internet connection. Click on your operating system for instructions on how to start in safe mode: Windows 10, Windows 8, Windows 7, Windows Vista, Windows XP, OSX

If safe mode for the operating system fixes the issue, there's other software in your computer that's causing problems. Possibilities include but not limited to: AV scanning, virus/malware, background downloads such as program updates.

Hi Matt - thanks for your advice. I did try starting TB in safe mode and that didn't change anything. When next I restart my operating system (Mac OS) I will take your advice and try that. -Ted

Hi SFHowes, Matt, or anyone else -

I finally had the time to reboot my Mac and unfortunately the safe mode restart did not change anything. If you have any other advice, I'm all ears. Otherwise I'll probably give up on Thunderbird within about a week because of work pressures.

thanks again for any pointers, -Ted

Update: a strange thing happened after I rebooted my Mac, then restarted TB. TB was able to read my office365.com email, yet TB was not able to send email via smtp.office365.com. After that I shut down TB and restarted it, and the original problem returned. TB cannot receive nor send via office365.com.

So a Mac reboot followed by a TB start may have allowed downloading email from office365.com, though this capability was lost with the next TB shutdown and restart.