--On Monday, April 18, 2011 13:19 +0100 Tony Finch
Murray S. Kucherawy<msk@xxxxxxxxxxxxx> wrote:
I don't think this work is targeted at intermediaries. In
fact, I'd be completely fine with expressly saying it's meant
to address processing at ingress MTAs only.
If you are going to make that kind of restriction, it should
happen at submission servers only.
There is a history of MX servers making "helpful" fix-ups to
messgaes (e.g. inserting missing message-id or from headers)
before handing them over to anti-spam software, which can make
spam/legit checks invalid in both the positive and negative
senses. So I think MXs should be as transparent as possible so
that downstream security software is less likely to have
interop problems. Intermediate relays should also be as
transparent as possible.
Of course, this is exactly what RFCs 4409, 5068, and 5321 say:
considerable flexibility for making fixes for the submission
server, which is presumably under the control of (or at least
responsible to) the sender; relays don't mess with message
contents until they get to the delivery server. Various
operational considerations have modified that somewhat but, if
this specification doesn't apply to intermediaries, it changes
nothing except, as Eric Burger points out, the practical
definition of well-formed messages.
IMO, if we want to do that (and I'd personally not favor it), we
should do so in some 5322bis, not try to sneak the changes in
via a BCP that is inconsistent with 5322.