This all sounds really good, as long as avast never ever have any sort of exploit in their code (Mozilla have many identified every year). They then undertake a sley of hand and thunderbitrd never actually gets to talk to the mail server, it talks o avast as a proxy. Real certifying authorities spend very large sums on certification and auditing. they have a renewed and valid certificate perhaps.Īvast has had you insert them a an SSL certifying authority. IT may well be one of the reasons your provider gets ansy when you ring. Disable email scanning and see the issue disappear into history. Your anti virus is, I would think, the actual root cause of your problems, not your mail provider or Thunderbird. and when I look to see if the exception I made is there, it's not or I'm looking in the wrong place. The problem is that TB is complaining about the cal.net cert. Turns out that quite a few certs expired in 2014 which is odd because I rebuilt my computer in 2015. I just went there and the page loaded just fine. It does not explain the cert problem which continues to elude me. In it is this 'By disabling ports 143 and 110, this removes completely STARTTLS as even an option for IMAP/POP connections.' So that explains my set-up. There is also an article that helps to explain why I'm so frustrated. I have attached some files to show you how I'm set up.

So from what I can see I don't have the option to NOT use SSL/TLS. Thunderbird appears to only offer SSL/TLS and STARTTLS.

Avast certificate error thunderbird