[Message redirected to ietf-822 because it's not talking about SMTP++]
Basically some intermediate node must try
to translate a message without knowledge of either the sender
or the receiver.
Assumably the translations will be well enough defined that it
can be performed "on the fly" by software.
You mean like from Chinese characters into English? Or from music and
pictures into ASCII? Or from an ISO ("ECMA") registration recorded last
Monday into Latin-1? :-(
No, doing so requires semantic knowledge. (I have a moderately strong
background in Linguistics, and know that language translation is a Hard
Problem). The kind of translations which can be done "on the fly"
are encoding funny bytes into printable ascii (eg UUENCODE, TEX-HEX, etc)
or (perhaps, if it is known) translating one picture (or sound) format
into another.
The last is something to be nervous over, especially over "conversions
with loss" (As X.400 puts it). Fortunately there are a couple of
headers available in X.400 (and codified into RFC parlance in Steve
Kille's string of RFCs ending in 1148)
Conversion: (allowed|prohibited)
Conversion-With-Loss: (allowed|prohibited)
Assuming that each piece of a message identifies what it is then
the sorts of conversions I'm talking about are doable.
What I expect is that as a message leaves an Enclave (as Stef described)
that anything funny about the body be translated into uuencode (or something).
Some sorts of markers need to be placed in the message describing what
each piece is, and the encoding be used. etc.
I'd be delighted to provide an MHS
with limit values on how much transformation I'm willing to let it do
(if you can define that scale), but the default ought to be that, if the
message can't be delivered as sent, it gets returned, not opened and
rewritten by some hidden daemon.
Are the Conversion: header lines enough for you? Suppose you had a
bitmap of some Known and Defined format in your message and the
destination was delivering messages to a fax machine. (Because the
person is away from the office, and messages are going to the hotel fax
where s/he is staying). Translating text into a FAX-bitmap is pretty
easy, supporting many character sets makes it a little bit harder.
Translating the bitmap is doable, but since G3-FAX is "only" 100x200
dpi then that translation might entail some loss in quality.
David