You appear to get a certificate exception prompt for imap.gmail.com. What is the exact error code you get? Please post a screenshot of the error you get.

Inspect the certificate - see the attached screenshot for instructions. Who's the issuer of the cert? Please post a screenshot of the Certificate Viewer window with the issuer information visible.

Also see this article for possible reasons for getting an exception prompt. https://support.mozilla.org/kb/add-security-exception

You'd need to explain in more detail how this is related to Yahoo though.

First of all thank you very much for your input.

Let me try to explain better. When i refresh my imap google mail box on port 993 with SSL/TLS protocol I get time to time a certificate error as Thunderbird told me Goggle SSL certificate issued by Google cert authority belong to Yahoo as shown on my screenshot. There is no error code but a Cert error as Thunderbird request me to add a security exception as the site (Google) try to identify itself with invalid information.

Certificate is issued " on the fly " so there is no local storage in Thunderbird's certificate manager and I didn't set any exception.

This may not related to the certificate issuer as I have same time to time same kind of trouble with other mail providers like Gandi. All my mail accounts are inside the same Thunderbird instance. Thunderbird tell me mail account provider i looking for is trying to use a wrong certificate belonging to any of my already previously set mail provider. Wrong certificate don't come randomly from nowhere but it belong to any mail account provider already set in Thunderbird.

It's look like Thunderbird or below application is looking owner's certificate in a wrong way.

Best regards,

I get time to time a certificate error as Thunderbird told me Goggle SSL certificate issued by Google cert authority belong to Yahoo as shown on my screenshot.

This may be your interpretation, however, from your screenshots I don't see any evidence that a cert issued by Google belongs to Yahoo.

Certificate is issued " on the fly "

You'd need to explain what that means. It could pretty much be the cause of your problem.

This may not related to the certificate issuer

Based on the information provided so far I'd say it is related to the certs issuer, therefore please provide that information as already asked above.

Wrong certificate don't come randomly from nowhere but it belong to any mail account provider already set in Thunderbird.

The cert is sent from your email provider's server. Thunderbird is then checking the entire certificate chain up to the root CA. Trusted CAs are built into the Thunderbird certificate store. By whatever means your 'on the fly' generated cert is issued, it almost certainly fails that check.

It's look like Thunderbird or below application is looking owner's certificate in a wrong way.

I doubt that, then everyone would see the problem, and I for one don't see that.

Nice if you can have a look :

1/ To Thunderbird preferences screenshot regarding certificates.Nothing is stored regarding Yahoo neither Gmail. That's why i said "on the fly" and also why I can't provide more information till next occurrence 2/ Written details regarding previous screenshot

Best regards,

Wrt your 2nd screenshot, that behavior sounds very odd, and something seems to be broken with your installation of Thunderbird. As a test I'd suggest you create a new profile, and then start Thunderbird with the new profile. Set up the Yahoo account as IMAP, and see whether you do get any certificate error or exception prompt.

Wrt your first screenshot showing the Thunderbird certifcate store: How did those certs get underneath the 'Server' tab? Did you deliberately put them there? If so, why?

Thank you for your suggestion regarding new profile you're right. I don't remember why there are certs under 'Server' tab even i put them here. Thank you for your kind help. I 'll update this topic if same issue occur with a new profile.

Take care !

Solved after updating libnss3-nnsdb. Have a look at https://developer.mozilla.org/en-US/docs/Mozilla/Projects/NSS for where it's used.

Finally issue was related to Dns resolution ! See my post 126425 on community letsencrypt org

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