Version numbering schemes aren't prevalent in Internet protocols
because they don't aid interoperability. Internet protocols use
deliberate open-endedness for controlled evolution and growth.
Version numbers are used to detect when non-interoperable changes have
Consider the possibilities were RFC 822 to have a version number, with
semantics similar to those suggested for MIME-Version:. What would
the acceptance of the MIME be if its incrementing the RFC 822 version
number caused various mailers to spew warnings and refuse to display
captions or compose replies without explicit user confirmation?
There will soon be a large installed base of MIME readers. The
probability that there will be a change that is not interoperable with
RFC 1341 readers is only slightly greater than the probability that
there will be a change that is not interoperable with RFC 822 readers.
scs(_at_)adam(_dot_)mit(_dot_)edu (Steve Summit) writes:
1. Received messages without a MIME-Version: header
should be treated in a fallback mode
MIME messages split into message/partial by an RFC 1341 composer, but
remerged by an draft-ietf-822ext-mime2-03 reader, will emerge without
a MIME-Version: header. This rule would then require some valid RFC
1341 messages to be handled in fallback mode.
A reader should not be required to examine the MIME-Version: header.
The header doesn't have enough utility to justify the implementation