Charles Lindsey <chl(_at_)clw(_dot_)cs(_dot_)man(_dot_)ac(_dot_)uk> writes:
This matter has recently been discussed extensively on the USEFOR
WG. The opinion seems to be that X-headers are more trouble than they
are worth (especially if they come into widespread use and widely
deployed software contains code that recognises them). It is also noted
that RFC 2822 no longer distinguishes them as a special case.
I agree with this part.
Current thinking on Usefor (as reflected in the current draft) is that
X-headers are appropriate for informative headers that are intended only
for human consumption (or for 'vanity' headers, and the like). There is
a blanket ban on standardizing them.
I agree with this part too.
And the recommendation for someone devising some experimental protocol
that is expected to require code in widely-deployed software is to use a
non-X header, whatever any standards might say. There are dangers in
this, but it is regarded as the lesser of the two evils.
I think that's an (unintentionally) misleading way of putting it. The
recommendation is that when someone gets ready to *deploy* a protocol over
e-mail outside of the originating organization or test base, they should
use a non-X name; in other words, as soon as people start putting
recognition of that name into normal software on a non-test basis, use of
the X name is inappropriate since it then creates unnecessary work in
future standardization.
But by the time the protocol extension reaches that point, it should
*already* be an I-D and the IETF consensus process can begin.
Exceptions of headers that reach widespread use without ever going through
IETF standardization can be dealt with separately. Encouraging people to
take that route rather than properly documenting their extension in an
IETF document strikes me as counter-productive.
I see no purpose served by the provisional registry.
--
Russ Allbery (rra(_at_)stanford(_dot_)edu)
<http://www.eyrie.org/~eagle/>