if you are getting the error immediately increasing the timeout is not going to help. Do you have anti virus scanning mail? Might be an idea to try it turned off.

Thank you for your reply. I have turned off both my antivirus and firewall....but it didn't help. Email provider created a email account for me via Outlook (on their end) to test - and was able to send/receive. I'm afraid this is beyond my understand of how to fix - I don't know what else to do. FRUSTRATED!!!

I checked my version of Thunderbird - it shows it was updated on Jan 26 to the currect version. It says this update fixed these issues - I don't know if they have anything to do with what's happening to me or not. However, Thunderbird worked fine for my mail email account up until about 2:00am morning the 30th.

fixed

Retrieval of S/MIME certificates from LDAP failed fixed

Address-parsing crash on some IMAP servers when preference mail.imap.use_envelope_cmd was set fixed

Incorrect forwarding of HTML messages caused SMTP servers to respond with a timeout fixed

Calendar: Various parts of the calendar UI stopped working when a second Thunderbird window opened

Well nobody addressed this issue. An accidental solution doesn't really help. I have exactly this issue and have been using the latest version since release [auto update] so for me that is not the problem . I used Mozbackup to install an earlier working profile with no luck. I even went back into 2019 to try a back up. I uninstalled and reinstalled [latest version downloaded today] TBird several times but can't get a working install. When I open set up an account and click email that opens set up an existing email account? Manual config is greyed out so you must enter at least your name and email in create existing account!! before you can open manual config. That opens a create existing account screen with all info from the existing domain name .msn of your existing email account. And this is manual configuration??? Okay. Click done and TBird accesses the server and says your profile has been found. Of course it does since you've input only data for an existing account! Click done on that and I get the bad username password or config error. You cannot create a new account which you need considering the old account isn't working. All of this derives from the original error of connection reset for which no solution was offered. So I am now faced with a TBird that won't work at all. I replied here since this was the only post purporting to address my our original problem. I can't fix TBird and can't set up a new account. So how do I actually create a new account? One final rant. TBird help is very very primitive. Search every word separately in any order and report every time every searched word appears? No context no nothing. I thought this sort of thing went out with XP. I expect this to result in no answer but perhaps a flame or two.