IECA Brute Squad Labs This document specifies conventions for X.509 certificate usage by Secure/Multipurpose Internet Mail Extensions (S/MIME) v3.2 agents. S/MIME provides a method to send and receive secure MIME messages, and certificates are an integral part of S/MIME agent processing. S/MIME agents validate certificates as described in RFC 5280, the Internet X.509 Public Key Infrastructure Certificate and CRL Profile. S/MIME agents must meet the certificate processing requirements in this document as well as those in RFC 5280. This document obsoletes RFC 3850. [STANDARDS-TRACK]