So I just started using a SSL POP3 server but Mail.app doesn't want to trust the root certificate. I've been able to find information about how to trust root certificates but nothing about how to retrieve the root certificate. I found a post that details how to retrieve the root certificate. Open the Terminal and type (all on one line):
For some reason openssl didn't like the port, so I had to change it from imaps to 995 (the port for POP3 SSL) as in:
openssl s_client -connect mail.dreamhost.com:imaps > dreamhost.cer < /dev/null
That gave me a file, dreamhost.cer, that could be imported into the X509Anchors keychain, as detailed in his post and several macosxhints.com entries that I was able to find.
openssl s_client -connect mail.dreamhost.com:995 > dreamhost.cer < /dev/null