OS X Mail claims Dreamhost mail certificate is for "localhost"


Lately on one of my machines when I launch Mail (this is OS X 10.8) it complains that the identity of my mailhost cannot be verified. It shows me a certificate for “localhost” (instead of for mail.dreamhost.com or anything similar), and it’s clearly a sample certificate: the contact email address is "postmaster@example.com". Obviously I don’t want to tell Mail to simply trust this certificate.

I contacted Dreamhost support, and they replied that they had accidentally had “localhost” certificates on my mail server group, but that they had fixed the problem weeks ago. Either they’ve missed one or my Mail app has cached the bad certificate. As I haven’t seen this warning on any of my other machines or devices, and I don’t see lots of complaints about it here, I suspect that the problem is a local cache. I don’t see any bad certificates in my keychain.

Anyone else seen this? Any suggestions for a solution? Thanks.