More user-visible goals

This one is necessary for any IETF effort, but I mention it anyway
to keep it visible from the start:

- users demand interoperability. A message should be usable regardless of
  the implementation used by the sender or recipient (provided both
  implementations are standards-conforming).

Being able to read referenced content in threads without having the
original material copied has already been mentioned.  Here is a related
issue:

- users want to be able to see relevant related material in context, in an
  appropriate order of presentation, and without having to read
  irrelevant parts of  previous exchanges.  [Yes, that means "top-posting
  is abhorrent" (possibly excepting languages where reading bottom-to-top
  is normal)]

- users want to be in control of the use of their resources (communications
  bandwidth usage, storage, execution of programs, etc.)  -- they don't
  want automatic execution of executable content from untrusted sources,
  for example.