I am using Thunderbird for e-mail in both Windows and Linux. The version is 140.1.1esr in Windows and 115.8.0esr in Linux (I didn't check that now, but that's what it is supposed to be for Xubuntu 22.04). Something like one month ago, I started having problems with both. Thunderbird wouldn't update inbox when I started it, except for some rare occasions. In Windows, it claims it connects to the server, but in Linux, it says it cannot. All this time, I have had no issues using e-mail on my smart phone with different client program. Thus, this is not about the service but about the client program. I am using IMAP and port 993 for incoming server and port 465 for outgoing server. Authentication is done using password and encryption is SSL/TLS. I don't remember if I had installed some update right before this started. What makes this especially weird to me is that the problem started in two different setups roughly the same time.