SSL error after server updated certificate?

Question

I posted about this elsewhere:
http://discussions.apple.com/thread.jspa?threadID=449770&tstart=0
but the basic problem is that my imap server updated its certificate (the old one expired) and now I cannot read email at all from Mail. I can definitely still read email from other apps (e.g. Evolution on Linux), but Mail.app seems permanently hosed.
When I click on the little !-inside-triangle-inside-circle I get a message that says:
The server error encountered was: An SSL error occurred while trying to read data from the server. How can I find out more about what's going wrong and more importantly, how to fix it!?
Powermac Dual 2.7 G5   Mac OS X (10.4.6)  

Answer 1

Actually, I was referring to the next subject in the Help list:
(I'm quoting)
Importing a personal certificate to use with Mail
Mail can encrypt email messages using the Secure Multipurpose Internet Mail Extension (S/MIME) standard for sending and receiving encrypted mail, verifying the sender's identity, and ensuring the message hasn't been tampered with.
You need a personal certificate to be able to sign and encrypt email messages. Certificates are issued by certification authorities, such as Thawte and VeriSign. The personal certificate may also be called a "secure email signing certificate," "digital certificate," "Certificate Authority key," "private key," "digital ID," "secure certificate," or a ".p12 file."
To get a certificate, first go to the certification authority's website, and create an account. Then request a certificate. You may need to pay for the certificate service. You can use Safari 1.2 or later to download certificates.
Certificates are stored in Keychain Access on your computer.
To import a personal certificate:
Double-click the certificate file you receive from the certification authority. Keychain Access opens and imports the certificate.
For Keychain Access to recognize a certificate file, it must have a file extension that indicates it contains certificates. Some examples of file extensions are .cer, .crt, .p12, and .p7c.
If Keychain Access does not import the certificate, drag the file onto the Keychain Access application icon, located in Applications/Utilities.
If you still can't import a certificate into Keychain Access, the certificate may have expired or the certificate may not be valid. Check with the certification authority.
You need a certificate for each of your email addresses. If you want to use the certificate on another computer, find and copy the original certificate you downloaded from the certification authority and move it to the other computer. Double-click the certificate file to open Keychain Access and import the certificate to that computer.