What do you see when you view the certificate? What site is named? Who is the issuer? When does it expire?

Another image might be the quickest response.

Clicking on the view button does nothing, I can't see any certificate. If i click Get certificate it then changes to say the certificate is valid but still can't view it when clicking the view button...

Ahh got the certificate this time. attached below

So your antivirus products self signed certificate is the issue. You will need to consult the McAfee documentation on how to include that in the Thunderbird certificate store. If you trust McAfee enough to give them access to all encrypted connections that is. I certainly don't.

I don't even have McAfee installed, so not sure where that is coming from...

if I click get certificate then view I get this

That was all weird to me, so I did the usual and googled. I saw other with the same sorts of issues on chromebook and pixel forums among other places. The one that struck me was one of the resolved and that person was a Verizon customer with a Verizon FIO router that was causing the issue. https://support.google.com/pixelbook/thread/148920224?hl=en&msgid=149041810

So I think what is needed is to ask you if you are also perhaps using Verizon, even in a third party way as a hotspot.

Pertinent is this 2019 announcement by McAfee of their inclusion in the Verizon router. https://www.mcafee.com/blogs/mcafee-news/verizon-teams-up-with-mcafee/

If that is not the issue, then we still have this announcement, also from McAfee indicating their software is embedded in routers from "D-Link, Arris, Verizon, CenturyLink, and others". So they do not offer a comprehensive list but hopefully that will be enough to track down the issue.

So I guess your are right and wrong. Your machine does not have McAfee installed, but some of your connection hardware probably does.

Please post back your findings on this. I am actually interested beyond the usual "support" thing.

Yes, I do have a verizon router. This has happened in the past and eventually went away on it's own but it is persisting now and very annoying. I appreciate you looking into this for me. This is not on a chromebook but rather on an LG PC. To note I'm not getting any errors of this sort using my iphone or mac, though not using thunderbird there. GoIng to check out the links you sent now. Sharon

I found the Mcafee home network controls and turned it off. Fingers crossed! Thanks again. Don't know why it just started happening though, it's been enabled for a long time,.

Which Thunderbird version are you using?

I'm asking, because there was a change in behavior in Thunderbird 128.

Which Thunderbird version are you using?

I'm asking, because there was a change in behavior in Thunderbird 128.

Version 115.10.1 (64-bit). No issues since I turned off the home network controls