I wrote before about using a secure connection to retrieve your email, using OS X’s Mail.app. The biggest problem was properly importing the secure certificate.
Well, it worked faithfully for me, right up until this evening. The certificate expired today, and a new one was issued. You cannot, however, import the new certificate without removing the old one. The existing certificate does not reside in any of the keychains that show up by default when you open Keychain Access.
After a bit of searching and misinformation, here was the solution:

  1. Open “Keychain Access”.
  2. Under the ‘File’ menu, select ‘Add keychain…’
  3. Navigate your way to the ‘System’ folder at the top level of your hard drive. Inside there, go to ‘Library’, and then go to ‘Keychains’.
  4. In that folder, open the ‘X509 Anchors’ file.
  5. When this keychain loads in ‘Keychain Access’, look through the list and delete the existing certificate.

From this point on, follow the steps in my original post to import the new keychain.