Re: "Importance" and "Priority"

[[e-mail]]

> 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".

I think you meant to say "Priority", rather than repeating "Importance".
However, "Priority" isn't really related to the other two.

> 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).

Correct, although whether these fields are intended to mean "Importance" or
"Priority" in the X.400 sense isn't clear to users -- I've seen both
interpretations demanded of the fields.

> 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.

It depends on what you think the fields mean and who you talk to. If, for
example, you think the fields are equivalent to X.400 "Importance", and thus
mean "how important the message sender thinks the message is", then I for one
assign the field no value whatsoeever.

> 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.

On the contrary, the meaning of all these fields is reasonably clear in 
X.400, and RFC 2156, as a simple mapping of field content, doesn't change
their meaning.

In particular:

   (1) Importance is an assessment of the message's importance assigned by the
       sender and interpreted by the receiever.
   (2) Sensitivity is an assessment of how sensitive the data in the message
       is, also assigned by the sender and interpreted by the receiver.
   (3) Priority is a routing/transfer/return indicator that is supposed to
       influence, among other things, the order in which messages are
       transferred and the amount of delay that can be tolerated before
       messages are returned.

> Existing Internet mailers, however, only
> seem to use these attributes in local mailers.

This is mostly true for "Importance" and "Sensitivity", but then, that's how
the fields are defined to work. But in the case of "Priority", this isn't
true at all. Exchange, for example, follows X.400 semantics fairly closely in
a lot of places, and that includes priority handling, at least in terms of
timeouts.

> Mail
> transmission today is so fast, that priority in
> transmission is probably not felt very much needed.

This isn't true either. Prioritized handling is a commonly requested and
frequently used feature.

				Ned