The certificate for inbound.att.net does not come from a trusted source.

Susan, I'm having this too. Do you happen to use AVG free anti-virus?

I don't think so, but don't really know.

I "think" I just found the culprit. I have AVG Free Anti Virus. Part of it is Email Shield. If I uncheck the Email Shield incoming messages start coming through Tbird.

oooh, let me know if it works!

where do I look for the antivirus program you referred to? (AVG Free Anti Virus)

I'm having the same problem. Not AVG; I'm using Paid Bitdefender. Looks like we need to depend on Mozilla for help on this one??

Susan yes, it did work for me. Click on the Start button (low left part of your screen) , then scroll all through the programs that show up. If you have AVG it will be a blue, green red, and yellow square. Click on it to open it. Click Menu in upper right. Then Settings. Then Basic Protection. Then Email Shield and uncheck the box Scan Inbound Emails.

Something odd must have happened with it because I've had that Scan Inbound Emails checked ever since I downloaded AVG. I can't explain it. It may clear up after some time passes. Who knows?

I have a Linux laptop. I scrolled through all the programs that showed up and I can't find any anti-virus programs, maybe I 'm not looking in the right place.

I to have Paid Bitdefender and can not get my emails and Yes Ito need hepl from Mozilla I've tryed bypassing Certificate validation

problem fixed

Go to Bitdefender "online threat prevention" and turn off "encrypted web scan"

Paulfaith, Thank you. I thought I had tried everything in Thunderbird, Bitdefender, and ATT. It's sad when we can't get help from any of the organizations. What worries me is: What changed to cause this problem? Everything was fine yesterday, and not good today. Both of the above fixes are really work-arounds. What is our vulnerability now? So many questions! Bottom Line: Thank you again. It's working!

Another Paul

One more thought: Susan, based on what I've read, it looks like jworks and both Pauls have a temporary fix. Are you still stuck? The real problem has to have initiated at ATT/Yahoo. The problem is spanning Operating Systems. All we're doing with the fixes is allowing a problem to pass thru the security to Thunderbird. If anyone finds the cause of this, please post so that we'll know what to look for next time.

Paul

hopfully the next update will have it fixed

I have yet to update my linux operating system, nor do I have the latest Thunderbird. I've been too scared of losing data and screwing up my archives ... Yes everything was working fine a day or two ago, then this message started popping up and I have to resort to getting my att.net mail on the website. I agree that .ATT/Yahoo is probably to blame.

I should either find a young person to walk me through the updates or get another "oldie" like me to help.

For now, I guess I'll limp along as I am doing until bravery strikes. Thanks everybody!

For what it's worth, I don't see how updating Linux or Thunderbird will make a difference. I have an old Windows 10 desktop and a new Windows 11 desktop, both with the latest Thunderbird release. They both have the problem. That's 3 different operating systems and different versions of Thunderbird all having the same problem. As paulfaith said earlier, maybe ATT's next release/update of their mail system will fix the problem. Or, maybe someone at Mozilla with expertise will feel sorry for us and chime in??

Thank you! I thought it was my own ignorance, but I do believe you are right. Different operating systems, Thunderbird versions, with the same problem. Common denominator: ATT. Again, thanks!