Hi, this issue is consistent across all my computers - home, work, laptop. At some point during the last couple of weeks, Thunderbird has suddenly stopped being able to connect to *some* IMAP mail servers and/or download messages. No settings have changed, and if I try to delete an account and set it back up again using the new account wizard, it appears to fail verification (username/password) even though they are 100% correct. I am able to connect OK using a different mail client on my smartphone, and it's only mail accounts on a particular server which fail to connect. I have several other email addresses on another server/host which still connect fine. The server settings are the same (apart from the server address and login info of course). All that appears in the notification area at the bottom left, is "Checking mail server capabilities". The accounts are using STARTTLS (port 143), but if I change the security to SSL/TLS (port 993) then it makes no difference. Only if i disable connection security is the connection established and the emails start coming through. Just to confirm, this has been working fine for 5+ years with the same mail server, no settings have changed from my end, and this literally started happening overnight. Accounts on other mail servers connect fine using the same connection security (which may point to the mail server software no longer being supported or something?) Please help, not keen on using an insecure connection. Thanks in advance.