As Keith pointed out, there are certain aspects of MTA filtering that
IETF should be concerned about, more than just having a single filtering
language endorsed to become an IETF standard. The aspects I am thinking
of is interoperability, predictability and security. It might help if we
can give consenting answers to the following questions:
How should a MUA be able to transfer filtering rules to the MTA (or more
precisely; to the delivery agent) so that arbitrary brands of MUA and
MTA can interoperate?
And, how can this be done in a way preventing evil attacks to succeed?
How can the MTA be able to communicate filtering status and reports to a
MUA in an interoperable way between arbitrary brands?
And, what can we do to eliminate unpredictable results from running the
filter rules?
If we are going to endorse a standard on MTA filtering, we have to
address the interoperability issue as percieved from site deployment
point of view. Or do you suggest that we are going to say, "Hey, it's up
to you to find the pieces that fit together"? Seem not to adhere to the
general spirit of IETF, IMHO.
To be able to answer the questions above, I suggest we either discuss
the possibility to define a simple TCP based protocol to be used to
exchange information related to MTA filtering. Or, discuss the
possibility to define one or more MIME based formats suitable to
exchange information related to MTA filtering using the mail transport
itself as communication media between the MTA and the MUA.
These are the only alternatives that, IMO, can lead to an eventual IETF
standard on the issue of MTA filtering. SIEVE can of course be part of
that efford as the descriptive language of filtering rules, but it will
not do by itself.
In my own words,
--Tomas