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Thunderbird 140.15.0esr does not find a manually imported S/MIME recipient certificate although it is correctly displayed under “People” in the Certificate Manager.

Thunderbird Encryption
Salute Training
Salute Training

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?

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?

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