NOTE
S/MIME is gaining in popularity in the enterprise because its key management facilities are implemented as a hierarchical public key infrastructure (PKI) scheme. Version 2 of S/MIME has gained some support and is defined by Request for Comments (RFC) 2311 through 2315. An Internet Engineering Task Force (IETF) working group is currently working on version 3, which is expected to become an Internet standard when it is completed.