S/MIME

S/MIME is a standard for signing and encrypting e-mail. It conforms to the following RFCs:

RFC 2632 S/MIME Version 3 Certificate Handling

RFC 2633 S/MIME Version 3 Message Specification

RFC 2634 Enhanced Security Services for S/MIME

While OpenPGP uses the so-called "Web of Trust" to ensure the validity of signatures and keys, S/MIME relies on certificates. You have to get a certificate from a CA before you can S/MIME-sign or encrypt messages within The Bat!.

The Bat! offers two S/MIME implementations: its own (internal) and the Microsoft CryptoAPI.