User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/85.0.4183.121 Safari/537.36

Steps to reproduce:

I have a dovecot server with a self signed certificate. This worked fine until 3 days ago, when I upgraded to 78.3.2 (I don't know the previous version I used).

I set Connection Security to StartTLS, Normal Password, Port 143 and try to retrieve messages.

Actual results:

Thunderbird is stuck at "Checking mail server capabilities"
In the server log, I get:
Oct 10 19:20:34 mail dovecot: imap-login: Disconnected (no auth attempts in 1 secs): user=<>, rip=$$$.$$$.$$$.$$$, lip=$$$.$$$.$$$.$$$, TLS: SSL_read failed: error:14094412:SSL routines:ssl3_read_bytes:sslv3 alert bad certificate: SSL alert number 42, session=<$$$$$$$$$$$>

The Thunderbird Error Log is empty.

Expected results:

Either retrieve my emails, or prompt me with the security prompt that I need to accept the self signed certificate. In a quite old version of thunderbird (68.12.1) it still works this way, and also in other mail applications.

Also, I just tried on 82 beta, but the behavior there is the same.