If you're getting that, it's almost certainly because you've configured the account to use a wrong mail server in Thunderbird. You shouldn't be getting that and you shouldn't have to add any security exceptions…

When I downloaded Thunderbird all I did was enter in the email address and TB did all the settings automatically. I just had to enter in password. I have used TB for about 3 years now, and periodically this security exception appears. It is quite easy to renew the certificate IF that popup window will appear. Now I am just getting a notice in the lower right hand corner where TB displays new incoming messages.

I can certainly give a try to change the email settings.

Good Day,

I manually edited the email settings in Thunderbird changing to what my domain host had in the email configuration page. Email is working. I have NO Idea why in the world I have never thought about editing the email server settings. Oh my heavens.

Thank you for your assistance.

Hello @DavidGG, I too am having this issue. As above, "when I downloaded Thunderbird all I did was enter in the email address and TB did all the settings automatically. I just had to enter in a password." I don't have access to the mail server and I cannot see anything wrong with the settings automatically entered by TB. Any ideas? Thanks

PS I've found the certificate for the mail server in the Certificate Manager under Let's Encrypt. The Certificate name = xxxx.net.au and the server = xxxx.org.au. Could this be the issue?

Hello @DavidGG, I too an having this issue. As above, "when I downloaded Thunderbird all I did was enter in the email address and TB did all the settings automatically. I just had to enter in a password." I cannot see anything wrong with the settings automatically entered by TB. I found the certificate in the Certificate Manager under Let's Encrypt. Could it be that the Certificate name= xxxx.net.au and the server = xxxx.org.au? If so, I assume the server owner will need to fix this, correct? Thanks

Hello @DavidGG, I too an having this issue. As above, "when I downloaded Thunderbird all I did was enter in the email address and TB did all the settings automatically. I just had to enter in a password." I cannot see anything wrong with the settings automatically entered by TB. I found the certificate in the Certificate Manager under Let's Encrypt. Could it be that the Certificate name= xxxx.net.au and the server = xxxx.org.au? If so, I assume the server owner will need to fix this, correct? Thanks

Good Day,

To resolve the issue, I manually edited the email settings in Thunderbird changing to what my domain host had in their email configuration help page. Email is working. That resolved the problem. Never had it again.