The certificate does not belong to to the server it is being used on. Why not use the correct certificate?

BTW as connection to the server is not functional, clearly the sent folder on the IMAP server will not be updated, so you get an error message to let you know.

Then HOW exactly can I use the correct certificate?

I logged in now, and I saw the first two images again! Since I click "Confirm Security exception" EVERY TIME that I log in and then I send my email properly, then why Thunderbird KEEPS poping up this message!

Since you seem to know, as you say, tell me the exact procedure that I need to follow, step by step, so that this messge doesn't popup again.

Why did you lock that topic? https://support.mozilla.org/en-US/questions/1321028

That topic is IRRELEVANT to this one, and your answer here gives ZERO information.

Open the other topic and give precise info on this one.

I locked it because this topic and that are both the same certificate issue. If I unlocked the other I would lock this and you would not like that either. So lets move forward. You have a single issue is my opinion. I see nothing that might indicate otherwise.

Please post the details of the certificate including the issuer and server it is issued for. Normally Avast self signed certificates go wrong because they are not issued by a certifying authority so either fail the oscp check that validates they authenticity and current validity or they raise issues about not being issued by a certifying authority. This is somewhat different in that it raises issues about the serve name not being correct. Without details of the actual certificate further comment or suggestions can simply not be made.

I can suggest. https://support.avast.com/en-my/article/Troubleshoot-invalid-email-certificate They put a nice twist on them using self signed certificate and the inherent risks they represent.

You are using port 143, this is not the default for SSL/TLS, and given you are also using anti virus product that scans connections. Can it do SSL/TLS on port 143? Normally SSL/TLS on IMAP would be Port 993 can Avast cope with this variation from "normal"? I don't know.

- I have a dedicated server with an SSL certificate generated through Cpanel. If you want further details then be precise on how I will copy-paste them here. - Even if I disable the Avast shields before opening Mozilla Thunderbird, then the "Confirm Security Exception" message still appears.

So let's see. I opened the link, went to the Avast site (I have the full license) and then Imported the Mail Shield. This is the result!

https://user-media-prod-cdn.itsre-sumo.mozilla.net/uploads/images/2021-01-09-02-21-42-bb0e66.png

Why are your developers torchuring users and they don't exchange a couple of emails with Avast to do this thing automatically? What are we? Some kind of developers?

I CAN'T read my emails again for 3 DAYS now!

Can someone from the Mozilla dev team speak with Avast and ask what is going on here? Because that thing worked only for 1 day. Then the same problems again and again. https://youtu.be/fVLOOLa15wQ

I did exactly what you said. Here you go: https://i.imgur.com/BgPiI1I.jpg

I also have a website in a shared hosting space and I can read my emails normally there. So maybe this is an SSL related issue compared with an Avast issue.

Can you enlighten me now? For 2 years our work is being delayed because you just can't put an option "Skip all Antiviruses" if that is really the problem.

Or your software can not co-operate with an SSL server. Something out of those two. Work on it asap!