A co-worker sent me some S/MIME signed email. With anyone else who has done this, the certificate has shown up in my login keychain. Not so with his. I wrote out the attached p7s file, and verified that it contains a sensible stack of certificates by using the open ssl command. I tried to use File/Import in keychain access. It 'succeeds' (no errors), but the certificate does not appear anywhere in keychain access.
I note that the p7s file has several certificates in it -- the signature chain up to the root. But that's supposed to be commonplace.
What could be wrong?