I've been using Thunderbird for ages without any (real) problems. My security certificate expired a few weeks ago, but now every time I try to retrieve my mail (by clicking "Get Messages") a pop-up appears (see image) The location (pop3.upcmail.nl:995) isn't the address of my mail server. If I look under Thunderbird's "Server Settings", I see the correct address. Even if I change the server address to something else, the pop-up 'add security exception' still displays pop3.upcmail.nl as location. I'm not worried this is some kind of hack or virus or malware since I recognize the address - it's the mail server I used well over ten years ago (in Thunderbird). I have checked so far: - cert_override.txt , but the wrong address is not in there. - Also disabled Eset, but did not solve. - the folder of my mailbox in profiles is called pop3.upcmail-1.nl (since i am using this map for over 10 years and changed providers a few times) Thunderbird keeps wanting to download a certificate from an over 10 year old and not in use mail server instead of my current one. Thus no e-mails are retrieved. So what is actually going on here? And more important, how can I solve this so I can get to my email again?