You are certainly not alone. I have the exact problem as you do and there are other users reporting same issues as well on the forum. Was running 68.12.0 fine but after updating to 78.2.2 three days ago, Thunderbird would no longer download new emails. Status bar showed it is online, when clicked on Get Messages, the status bar displayed "Connected to" my email server but somehow the connect was reset and not proceeding to say "Host contacted, sending login information" or "Checking inbox for new messages".

Was using POP3 account server setting before but tried IMAP as well but still would not work.

Now I've installed an older version Thunderbird 68.9.0 (32-bit version as I'm running Win10 32-bit OS) from the Thunderbird releases download page. Needed to create a new profile as my original profile cannot be re-used in an older version after running 78.2.2. At least I'm able to download new emails from my ISP email server again with 68.9.0.

I can get by downloading emails for now but hopefully, someone can provide a solution or further 78.x updates will fix the problem.

Thanks Anthony.

I'm using IMAP.

It's good to know it's not just me!

I have switched to MS Outlook (perhaps temporarily...perhaps not) and that works perfectly.

Regards, Jim

Since upgrading to 78.2.2 I don't receive new messages. I can read old messages in any folder. I can send OK.

Some users mention that a workaround is by toggling the value of the option security.tls.version.min from 3 (or 2) to 1. Would it help?

Thanks for the suggestion. I shall give it a try when I get a chance to reinstall Thunderbird.

Jim

see https://support.mozilla.org/en-US/kb/thunderbird-78-faq#w_after-upgrading-to-thunderbird-78-i-cannot-get-or-send-email-messages