Fredly wrote:

I like the Thawte free option...

I thought the Thawte certificate is free only for personal use and not for
use in a business environment, but checking their web site doesn't seem to
indicate there are any restrictions of that type. It's certainly an option.

There is also a free GnuPG encryption application that is the Gnu version of
PGP (which was purchased by a company) and there's an Outlook plug-in for
GPG.
--
Brian Tillman