Outlook and outlook express support digital signing and encryption -- but one must first get a certificate.
Now what I want is a certificate that merely asserts that the holder of the certificate can receive email at such and such an address, and that only one such certificate has been issued for that address. Such a certification system has very low costs for issuer and recipient, and because it is a nym certificate, no loss of privacy. then generate one. it won't be accepted as legitimate by the majority of clients though - you would have to get each one to approve you manually (like you would with a pgp key, but without the WoT to help you) keys can be generated using OpenSSL, or if you aren't a fan of command line tools, EBCrypt can generate them from VB; there is a mini-ca script here: http://groups.yahoo.com/group/WSH-CA/files/Current/ if you want to play with it :)