Mozilla Thunderbird/directory certificate not trusted
If you get an error message while typing an email address that reads directory.education.ucsb.edu:636 uses an invalid security certificate and reports Error code: sec_error_expired_issuer_certificate, these instructions should help you fix it.
Trust the directory certificate
Open Thunderbird, then click Write to compose a message.
Type an email address. Enter your password if prompted. When the error message appears, STOP!
Click View Certificate.
Click the Details tab, then click the Export... button.
Save the file to your Desktop
Click Close. Click Cancel.
Now, click Thunderbird → Preferences...
Click Advanced → Certificates → View Certificates
Click the Servers tab, then click Import...
Find and open the file you saved. It's probably called directory.education.ucsb.edu.
Select the certificate and click Edit...
Check the Trust the authenticity of this certificate. box, and click OK.
Click OK, then close the Preferences dialog.