The certificate for mobile.charter.net:993 does not come from a trusted source.

Identical problem @gschaben1, including the result of requesting an exception.

I seem to remember this happening once years ago. I'm hoping maybe a nightly builds might fix it.

There is a third complaint about what sounds like the same thing. See this thread:

https://support.mozilla.org/en-US/questions/1586525

Certificate problems like this are usually due to misconfigured or malfunctioning servers. That there are multiple complaints suggests to me that it's an issue on Charter's end. Has anyone contacted them to see if they are having a known problem?

here's my experience TB + Charter ok in W10 Doesn't work in W11 or Gmail on an android phone Began wonkiness 6/9/26

One call to spectrum didn't get anywhere, Going back to the plate to swing again with your coaching.

It's seems like it is a certificate issue. Thunderbird on my Windows 11 PC at home with the same version of Thunderbird works fine, but the View Certificate window has two tabs in addition to the mail.charter.net Certificate tab that are completely missing on my work PC (the one with the problem). The first tab is titled GlobalSign RSA OV SSL CA 2018 and has this as the first two sections: Validity Not Before Wed, 21 Nov 2018 00:00:00 GMT Not After Tue, 21 Nov 2028 00:00:00 GMT

Subject Name Country BE Organization GlobalSign nv-sa Common Name GlobalSign RSA OV SSL CA 2018

and the second tab title Issuer Name is populated by this: Subject Name Organizational Unit GlobalSign Root CA - R3 Organization GlobalSign Common Name GlobalSign Issuer Name Organizational Unit GlobalSign Root CA - R3 Organization GlobalSign Common Name GlobalSign Validity Not Before Wed, 18 Mar 2009 10:00:00 GMT Not After Sun, 18 Mar 2029 10:00:00 GMT

There are several GlobalSign certs in the Certificate Manager, including a Root CA - R3 cert with trust settings for identifying both websites and mail users, but I don't know why it's not showing in the View Certificate window, or how to install/move/get it to show up there.

Another oddity: changing the Connection security from SSL/TLS to STARTTLS gets rid of the 'The certificate for mobile.charter.net:993 does not come from a trusted source.' warning, but generates a 'Connection to server mobile.charter.net:143 failed.' error when testing the server in Account Settings.

And now it seems to be fixed. No warning on the account line on the home screen, and testing the connection to the server returns 'Successfully established a secure connection to mobile.charter.net:993.

And now it seems to be fixed. No warning on the account line on the home screen, and testing the connection to the server returns 'Successfully established a secure connection to mobile.charter.net:993.

And I see a couple of the other complaints also saying it's working again. That seems to support my feeling that it was a server or network issue. Well, all's well that ends well... if it's truly ended...