Apple should really document some things better.
Since 10.3 mail.app warns for self signed certificates.
Very annoying, esp. for the less savy user.

On my new iBook, I created a new Keychain and thus lost any custom certificates.
After 3 days, clicking through 4 warnings every time you start up mail.app becomes annoying, even on a jiffy G4.

The solution however, is surprisingly simple (much simpler than I recall at least from the previous time.)

Make sure you have your certificate in a plain textfile, for instance imapcert.crt.
<br /> #sudo /usr/bin/certtool i imapcert.crt v k=/System/Library/Keychains/X509Anchors<br /> ...certificate successfully imported.<br />

That’s all folks!

Credits go to: whoopis.com

Update 9 mar 05
In my current Panther Server this method fails,
<br /> ***Error getting keychain handle : SecKeychainGetDLDBHandle: SecNoSuchKeychain<br />

Googling and ADC doesn’t bring up anything helpfull.
However,drag’n’drop does work as well.
Just throw your .crt on the keychain.app and make sure you select X509 anchors to import to.

I really think mail.app should handle this properly instead of f (bad word) around with keychain.app