Thunderbird Community Forum

Thunderbird has worked fine for me over the years. I rarely send mail but started receiving a message that smpt server refused connection and contacted Network Solutions support. Their advice is below but I have clicked Clear Security Exception many times but can't get beyond it. Any ideas would be welcome.

To configure your mailbox in Thunderbird, please follow these steps:

   Open the Thunderbird application.
   Select Add Mail Account.
   Enter your Full Name, Email Address, and Password.
   Click Continue. 
   When you reach the page titled "Connect your email settings", click Edit Configuration.
   Change both the Incoming Server Hostname and Outgoing Server Hostname to mymail2.myregisteredsite.com.
   Click Connect.
   Enter your mailbox password when prompted.
   After entering the password, a warning message may appear. Select Confirm Security Exception.

Please note that you may need to click Confirm Security Exception three or four times before the account setup is completed successfully.

The reason you are receiving the security warning is that the mailbox is configured to use Connection Security: None. This is necessary because your mailbox is hosted on a legacy email service that is not compatible with SSL/TLS or STARTTLS encrypted connection methods. As a result, Thunderbird may display security warnings during the configuration process.

If you require further assistance with Thunderbird configuration, we recommend contacting your personal IT professional or someone familiar with email client setup and administration, as third-party email client configuration falls outside our support scope.

After upgrade to thunderbird 153.5.1esr from 140.17.0esr on a debian 13 (trixie) system I can no longer digitally sign my message with my external OpenPGP key located on a smartcard: I get the error message "Unable to send the message, because there is a problem with your personal key. The configured key ID ‘...’ cannot be found on your keyring." If I try to import the public key via the OpenPGP Key Manager I will get the alert "Importing the keys failed. TypeError: RNPLib.prepare_ffi is not a function". Any idea how to fix this?

Hello,

Since I updated Thunderbird to the version 153.5.1esr (64 bits) on Debian, I can't access to my PGP keys anymore, so I can't encrypt/decrypt my mails with OpenPGP.

In the console, I found this error message when starting Thunderbird: Error: RNP/OpenPGP library failed to load

And in OpenPGP, when I try to import keys (in .asc format), I've got this error message TypeError: RNPLib.prepare_ffi is not a function

I'm lost and I couldn't find any relevant information about this error for this version.

What can I do ?

What do I do about this warning I am receiving when I refresh my inbox? "The certificate for pop.windstream.net is not valid. Someone could be trying to impersonate the server and you should not continue"

   Unable to receive new messages on my Thunderbird inbox for this warning

What do I do about this warning I am receiving when I refresh my inbox? "The certificate for pop.windstream.net is not valid. Someone could be trying to impersonate the server and you should not continue"

   Unable to receive new messages on my Thunderbird inbox for this warning

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?

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.

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 :)

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?

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