Both
2421 Voice Profile for Internet Mail - version 2. G. Vaudreuil, G.
Parsons. September 1998. (Format: TXT=123663 bytes) (Obsoletes
RFC1911) (Status: PROPOSED STANDARD)
and
2156 MIXER (Mime Internet X.400 Enhanced Relay): Mapping between X.400
and RFC 822/MIME. S. Kille. January 1998. (Format: TXT=280385 bytes)
(Obsoletes RFC0987, RFC1026, RFC1138, RFC1148, RFC1327, RFC1495)
(Updates RFC0822) (Status: PROPOSED STANDARD)
specify two useful e-mail header fields: "Sensitivity" and
"Importance". RFC 2156 also has a related header field
"Importance".
Such fields are obviously felt important by several mailer
developers, since they use various own headers for this,
such as X-Priority (Eudora) or X-MSMail-Priority
(Microsoft).
As an e-mail user, I often send and get messages in which
we do use the X-Priority heading, even though they only
work between certain mailers, so this heading is also
obviously felt useful by many people. Very few messages
indicate a lower than normal priority, the usage is
almost only to indicate a higher than normal priority
for some messages.
RFC 2156 defines importance as:
importance = "low" / "normal" / "high"
and priority as:
priority = "normal" / "non-urgent" / "urgent"
The difference between these fields is not very clear
from RFC 2156, but in X.400, priority is an envelope
attribute, while importance is a heading attribute,
so presumably priority is meant to be able to influence
transmission. Existing Internet mailers, however, only
seem to use these attributes in local mailers. Mail
transmission today is so fast, that priority in
transmission is probably not felt very much needed.
--
Jacob Palme <jpalme(_at_)dsv(_dot_)su(_dot_)se> (Stockholm University and KTH)
for more info see URL: http://www.dsv.su.se/jpalme/