I am trying to send encrypted email to recipient. This person has changed their email address. Let's suppose it used to be bob@email.com and now it's robert.t.bruce@email.com Because they are still who they have always been, there's a newer certificate with different expiration date and email, but has same name. Anyway, I hit reply to the person's signed email they sent me. Thunderbird "can't find" a certificate for that person. Despite that certificate sitting there in my inbox. If I go in to the certificate manager, I see that there's a certificate for him under his old email address like BRUCE.ROBERT.123456 bob@email.com Now get this: I delete that certificate. Am I sure? Yes. Close and open the manager, and that certificate is gone. Deleted, right? I go back to my inbox. I view the certificate he signed the email with, it has the same name BRUCE.ROBERT.123456, but the email address is now the new and correct robert.t.bruce@email.com So I Export this certificate to BruceRobert123456.cer file. And I open certificate manager and Import that certificate .cer file. I close and re-open certificate manager and, hey, it's not there. I just imported it, but it's not listed. Very weird. I go back to my Inbox, again hit reply to his signed email and I get the same problem, certificate not found for robert.t.bruce@email.com. If I go into certificate manager, the evil, old certificate with bob@email.com has re-appeared! How can this be? Where in the world is this coming from? Where did Thunderbird get the old certificate from??? This is maddening, failed software.