I think Bruce has correctly pointed out that there is an existing mechanism
whose
precise purpose in life is to accomodate such obsolescence changes.
Let me also add that the idea of a huge impact on thousands or millions of
users
because of a minor change is overblown. People don't wake up one morning
and
discover there's a new RFC or an RFC in a new state, delete their existing
copies
of Outlook or Eudora or sendmail or whatever, and sit around without
email for weeks or months waiting for the world to catch up.
What happens is that the folks at Qualcomm and Microsoft and the open source
community and whereever else put out new releases. In some cases, they use
it
as a selling point to make more money. In other cases, such as the open
source
community, they use it to help prove their faithfulness and quality. They
do so
without breaking existing stuff catastrophically, just as existing web
servers still
support HTTP 1.0 in spite of incompatibilities with HTTP 1.1.
Eventually things get to be so obsolete that people are forced to upgrade,
e.g.
version 1 of Netscape or IE. Or they continue to work with rough edges,
e.g.
the folks still using version 4. But the world doesn't end and email won't
break
down.
Gary