Overview: S/MIME Building Blocks
RFC 822: Internet Text Message Format
RFC 821: Simple Mail Transfer Protocol (SMTP)
S/MIME Services Are Layered On Top of MIME and “Classic” E-Mail
RFC 2633: S/MIMEv3, Using RFC 2630: CMS
Signed (Two Forms) Encrypted
CMS Signed Data RFC 1847 Security Multipart CMS Enveloped Data