For those of you who might not be aware of what S/MIME (Secure/Multipurpose Internet Mail Extensions) is, this short description might be helpful.
As most of you are aware, messages or e-mails, in general, are mostly insecure if they are not digitally signed and their transport isn't encrypted. With S/MIME, the messages can be digitally signed, which can be seen as a guarantee that the sender is the person they claim to be and not anyone else. With the use of S/MIME, the contents and attachments of messages can be encrypted.
In Exchange 2013 RTM, the support for S/MIME was removed for OWA, but it was brought back when Service Pack 1 was released, which was great.
For this recipe, I've decided to use an internal PKI solution ...