[Djigzo users] encrypted email in the cloud

After reading this article below: https://www.ciphermail.com/blog/encrypted-email-in-the-cloud.html it describes how to setup ciphermail to encrypt all email before forwarding to its final destination. I have a couple of questions. This article talks about PGP encryption, could the same thing be done using s/mime encryption? It also doesn't mention if the recipient should be set to internal or external? I'm assuming internal. Thanks Dino