I'll take a guess that the message you haven't been able to copy is one advising you that the security certificate has lapsed or is invalid - and then it asks you to verify that you wish to proceed with an insecure connection.

If that's the message, the bottom line is that it's up to you whether you connect to a server that isn't validated. I wouldn't recommend it.

But it’s the same server I’ve had for decades. I guess I don’t really understand what a Certificate is. Is that something I take up with the service provider?

I’ve never had it happen before. Only thing new is I set up Apple Pay yesterday, but I have no idea how that would interfere. I was getting all the prompts and codes from my email to do that.set up.

Nope, I can't explain it or understand it, either, But here's a link to a file (which still makes no real *technical* sense to me after reading it):

https://sectigostore.com/page/what-is-ssl-server-certificate/

The bottom line is that the security certificate validates the integrity and safety of the server that you're trying to connect to. The problem seems to be with the server and the email provider - not with Thunderbird and not with you.

I would suggest to contact your email provider.

Hopefully, if I'm off in my understanding of the matter, a more experienced forum user will correct me.

I have linked to an external web page so my reply has to go through a moderator. Apologies for the delay.