[1] RFC 2046 - Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types ( 版) <http://tools.ietf.org/html/rfc2046#section-5.2.3.5>
[2] RFC 2046 - Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types ( 版) <http://tools.ietf.org/html/rfc2046#section-5.2.3.6>
Given the potential for
abuse, any such request messages that are constructed
should contain a clear indication that they were
generated automatically (e.g. in a Comments: header
field) in an attempt to resolve a MIME
"message/external-body" reference.