RFC 822: Standard for the Format of ARPA Internet Text Messages
RFC 1123: Requirements for Internet Hosts -- Application and Support
RFC 1521: MIME Part One
RFC 1566: Mail Monitoring MIB
RFC 1891: SMTP Service Extension for Delivery Status Notifications
RFC 1892: The Multipart/Report Content Type for the Reporting of Mail System Administrative Messages
RFC 1894: An Extensible Message Format for Delivery Status Notifications
RFC 1895: The Application/CALS-1840 Content-type
RFC 2045: Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies
RFC 2046: Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types
RFC 2047: MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text
RFC 2048: Multipurpose Internet Mail Extensions (MIME) Part Four: Registration Procedures
RFC 2049: Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and Examples