[Cryptography] Any S/MIME or PGP for normal people

[John Levine]

An acquainance of mine would like to set up some sort of message
signing within a small business to make it easier for the staff to
recognize real mail among each other.  I told him I'm not aware of any
non-toy installations that aren't either in the government or a giant
business that can mandate specific S/MIME software and configure it to
use their favorite CA, or else a bunch of crypto nerds.

Before I tell him to give up and use DKIM and DMARC, is there anything
I can point him at that grandma could use?

R's,
John