I installed a certificate on the mail server with Subject Alternative Names. Thunderbird does not throw any warnings but when an Outlook 2007 client connects, it throws a warning titled, "Internet Security Warning - The target principal name is incorrect | View Certificate | Do you want to continue using this server?"

I viewed the certificate and went to details, and it has six domains in the Subject Alternative Name field. That list includes the exact DNS name that I have listed for imap and smtp servers.

If I change the imap and smtp to the primary DNS name that the certificate was Issued To, then the error goes away.

Why does Thunderbird understand the Subject Alternative Names but Outlook throws the warning?

Also, I'm using USGCB group policies. I haven't been able to find anything so far... is there a windows server 2012 group policy that might be removing support for Subject Alternative Names in a UCC?

The certificate was purchased from go-daddy.

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