Can not digitally sign messages with Thunderbird


I created and downloaded a personal email certificate. I imported it to keychain, and exported it as pk12, and imported it into thunderbird again. However, I can’t sign any messages, I always get the error:
“Unable to sign message. Please check that the certificates specified in Mail & Newsgroups Account Settings for this mail account are valid and trusted”

In the settings I see the certificates, but I also see the error message “could not verify certificate for unknown reasons”.

Is there anything I forgot to do?

I am on Macos 10.8.4, Thunderbird 17. Same cert works with Mac Mail.
regards and thanks!


Check the knowledge base to see if the answer is there:,128,96

If not, post back.


Hello, I checked and I think it doesn’t apply.

  1. I imported the certificates into thunderbird (two for two mail accounts).
  2. I can see certificates in the overview
  3. If I click on a certificate I get the error “couldn’t verify this certificate for unknown reasons”
  4. I can not digitally sign an email (error screen attached)
    I have imported the certificates into keychain
    I can digitally sign an email from Mac Mail program. So I think the problem is not certificate itself, but Thunderbird + this certificate.
    I have used thawte certificates in the past and it worked.
    I am using webpg for digitally signing.

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The most common reason for this type of error is that during the export it was not specified to export all the certificates in the chain.
Therefore, when imported it is not trusted.

Or, your not using the exact email address the certificate is for, worth reading this knowledge base article:,128,96,32


I exported it from keychain there is no option to export or not to export all certificates in the chain.
I am using it with exact the same address. As I said before it actually works in MacMail.


It might be worth revoking the certificate, and going through the application process again.
Then trying the export, import.

This can be done by following this:,128,96,32

If that doesn’t work, contact support to see if applications for free email certificates can be made using a Mac, I know it used to be Windows only but that might have changed.