Mail Certificate Problem?

I'm at Cleveland State University. We just switched over to a Microsoft IMAP service. I have learning disabilities, so I need to be able to use the mail clients on my computer to work effectively - a web client is NOT an option. I had my CSU email set up in all of my web clients successfully. Then, one day, *almost* all of my clients stopped working. My Apple Mail and my iPhone all stopped connecting. I don't get it.

I poked around in Terminal and ran the following command with the following result:

Kompu7:~ jaime$ openssl s_client -connect pod51019.outlook.com:993 -ssl3 -crlf -quiet

depth=2 /CN=Microsoft Internet Authority

verify error:num=20:unable to get local issuer certificate

verify return:0

* OK The Microsoft Exchange IMAP4 service is ready.

Here is a really tricky detail. Thunderbird running on the same user side as my failed Apple Mail connection is able to connect and cache mail just fine. So... what are these Apple products experiencing that Thunderbird is immune to? And how do I get the Apple Mail and iPhone back on track?

Thanks