Thunderbird Community Forum

Thunderbird will not download mail. It sends this: "The certificate for inbound.att.net does not come from a trusted source." "Location: inbound.att.net:995" Then it sends the data with the certificate information. I am not a programmer, I do not understand what I am supposed to do to get it going again.

AVG sends message: "We've identified a site certificate problem" "Trust for this certificate has been revoked."

Looking at certificate page that AVG provides is Greek to me. General tab displays:

"This certificate has been revoked by its certification authority"

issued to : inbound.att.net

issued by: Digicert Global G2 TLS RSA SHA256 20250 CA1

Valid from: 4/12/26 to 10/28/26

Details tab:

lists a bunch of things that I don't comprehend and offers an option to "copy to file" and lists a number of formats to copy the file to.  Have no idea which would be the one to use. 

Trying to access email directly from browser has not been successful because it wants verify my identity by sending message to my phone, but it does not send anything.

I have Thunderbird installed on Windows 11 along with Norton 360. Today, my connection to the AT&T e-mail server suddenly disconnected and I immediately got a pop-up notification that Norton detected a problem with a security certificate. When I inspected the details, it indicated that the certificate for inbound.att.net had expired (the range of valid dates on the certificate actually listed the current date as the last valid date). After several infuriating calls with AT&T support and Norton support, I figured out that simply disabling Norton e-mail protection allowed me to access my e-mail account.

Multiple web searches on similar issues suggested that since Thunderbird has its own certificate storage, fixing the problem involves locating the Norton certificate file and importing it using Thunderbird's certificate manager. Unfortunately, that solution appears to be applicable for first-time Thunderbird installation, and I when I tried it I was informed that the certificate was already installed. Another web search suggested that I should go to the Authorities tab and remove the entry for "Norton Email Protection". Unfortunately, the entry that I found was for "Norton Web/Mail Shield", which according to at least one source is not the same thing, so I am afraid to remove it.

So my question is has anyone else encountered this same problem, and is the correct approach to remove the Norton Web/Mail Shield authority before importing Norton's certificate file?

Norton flags that the Thunderbird certificate has expired. Looked at instructions on the help, but most are to start from scratch. This is a new problem as of today, so fairly sure it isn't on my end, but cannot verify.

We are not getting emails because we keep getting an error message which reads The certificate for imap.shaw.ca does not come from a trusted source.

I am trying to send an S/MIME encrypted email from Thunderbird to:

jobcenter-chemnitz.netzwerkpartner@jobcenter-ge.de

The recipient certificate is provided by the official certificate directory of the German Federal Employment Agency (Bundesagentur für Arbeit).

I downloaded the recipient certificate and successfully imported it into Thunderbird under:

Settings → Privacy & Security → Certificates → Manage Certificates → People

The certificate is displayed correctly there. The email address contained in the certificate is:

jobcenter-chemnitz.netzwerkpartner@jobcenter-ge.de

The certificate is valid from July 29, 2026 to July 29, 2028 and includes E-mail Protection and Key Encipherment.

The required CA certificates are also installed:

BA-Class-1-Root-CA-4:PN BA-VPS-CA-11:PN

However, when I compose an encrypted email to this exact address, Thunderbird reports:

“You have selected to encrypt this message, but the application failed to find an encryption certificate for jobcenter-chemnitz.netzwerkpartner@jobcenter-ge.de.”

Under S/MIME → Recipient Certificates, Thunderbird also shows the certificate as “Not found”.

I have already tried:

deleting and re-importing the recipient certificate completely restarting Thunderbird after importing it manually typing the recipient address in lowercase without using autocomplete checking the complete CA certificate chain temporarily disabling OCSP

None of these changed the result.

My own personal S/MIME certificate works correctly. As a test, I can compose an encrypted email to my own email address without any certificate error. Therefore, the basic S/MIME configuration and my own certificate appear to be working.

When I reproduce the problem with the Thunderbird Error Console open, I get:

NS_ERROR_ILLEGAL_VALUE (0x80070057)

related to:

nsIMsgComposeSecure.beginCryptoEncapsulation

This seems similar to Mozilla Bug 2021265, where a manually imported recipient certificate is visible in Certificate Manager but is not found when composing an encrypted message.

Is this a known issue in Thunderbird 140 ESR, and is there a workaround for using this manually imported recipient certificate?

Hi there.

I'm in Alberta, where we have recently changed timezones. Note that the CLOCK has not changed yet, as we are still before the date in November when we would "fall back". We were UTC-6 summer and UTC-7 winter. Windows called this "Mountain Time (USA and Canada), but now the "Mountain Time (Alberta)" timezone is in Windows after the 2026-09 Preview Update (KB5124010) (26300.9550).

When connecting to Shaw.ca's IMAP servers, the certificates that were valid prior to the Windows update are now reported as invalid. This has been confirmed across two separate PCs with different email accounts. The data for the certificate LOOKS valid (see screenshot) and is the same before and after the timezone change.

The failure occurred on the latest ESR release of Thunderbird, as well as 156.0 and 157.0 non-ESR.

Thanks :)

Thunderbird email says the certificate for my Shaw email server does not come from trusted source. The certificate looks fine. I cannot get Thunderbird to "Add exception". The certificate issue seems to be an intermittent problem since yesterday lunchtime. It started working again yesterday afternoon, but stopped working at lunchtime today. How do I stop this error?

Hi,

I remember i tried 7y. ago a email certificate signed with SHA3, it was not OK.

I tried again now, and it is still blocked.

1) the certs can be added in the account settings > S/MIME for signature and ciphering, with a warning. 2) then creating a new email, the recipients certificates are not detected (while configured in another account on the same thunderbird client), and forcing ciphering is not allowed with the error message

"Sending of the message failed. This message cannot be digitally signed because the signing certificate selected in your End-to-End Encryption settings is not valid for this operation. (The certificate was signed using a signature algorithm that is disabled because it is not secure.)"

"Unable to save your message as a draft. This message cannot be digitally signed because the signing certificate selected in your End-to-End Encryption settings is not valid for this operation. (The certificate was signed using a signature algorithm that is disabled because it is not secure.)"

Even, when using only ciphering, and no signature in S/MIME.

The parameter mail.smime.accept_insecure_sha1_message_signatures do not change the bahavior.

-> Can Thunderbird allow SHA3 usage, please ?

Even if thunderbird does not want to generalize it, mozilla may create a parameter by default false

mail.smime.accept_sha3_message_signatures

Best Regards, Gwenolé

I am using an email server that currently is using certificates that have expired. That problem is being worked on. In the meantime, whenever I access the server to open a folder, I get a pop-up notification telling me that the certificate has expired. I go ahead and confirm the security exception and check the box to permanently store the exception. Trouble is this ISN'T being persisted, when I open a different folder I have to go through this process again in order to access my emails in that folder.

Me thinks you got a bug in your software Kemosabe!

I can't get my e-mails today. I got a message saying The certificate for pop.centurylink.net is not valid for that server. Someone could be trying to impersonate the server and you should not continue.

Why did I get this message? I never saw this before. I like to get my e-mails. I tried reseting my router and turned off my computer and it still says the same thing. What do I do and how will I see your reply if I can't get the e-mails? Please fix this. My e-mail is toosmiley@centurylink.net

Thank you

I can't find the certificate in order to delete/distrust it. Its name is my mail server. Organization: Lumen Technologies, Monroe, Louisiana

Subject Name Country US State/ProvinceLouisiana LocalityMonroe Organization Common Name Lumen Technologies, Inc. mail.centurylink.net Issuer Name Country Organization Common Name US DigiCert Inc DigiCert Global G2 TLS RSA SHA256 2020 CA1 Validity Not BeforeWed, 27 Aug 2025 00:00:00 GMT Not AfterSun, 27 Sep 2026 23:59:59 GMT

In Plain English how to use and secure encryption on all outgoing emails please and whether or not to use this great advantage. Many thanks to all those who contribute to this work, PB

https not recognized by Firefox in 151 Thunderbird on silicon iMac with Sonoma. Tried & checked many solutions with no results.

Firefox browser primary , always Nothing in Modified Important Preferences With Extensions off still a problem

Receive popup message: The certificate for mobile.charter.net does not come from a trusted source. In trying to send email, popup message: Sending the email failed. Peer's Certificate issuer is not recognized. The configuration related to mobile.charter.net must be corrected. Then it wants me to Add Security, Get Certificate.

Hi

I have a problem with Thunderbird which might be a bit niche but here goes...

The first attempt at sending an email fails as TLS Record Layer v1 is used, the mail server sees this and hard resets the connection so sending halts. See attached Wireshark trace screenshot "Failed".

If I retry the send again Thunderbird uses TLS Record Layer v1.3 and the email goes out ok. See attached Wireshark trace screenshot "Success".

If I send another message immediately no problem but if I wait 20-30 minutes the above cycle happens again.

I have set the minimum TLS version in the config to 1.3 (option 4) and restarted Thunderbird but this has not changed anything.

Any ideas how I can fix this? It's a pain because automated replies don't work.

Mozilla suddenly says "The certificate for mobile.charter.net does not come from a trusted source." It will not let me get my emails. Is this a problem with Thunderbird or Charter (Spectrum) I am able to receive email on my I Phone. I do not know which Thunderbird version and can't find it using your instructions. Help please