Is this really a big enough problem to be worth solving? I can't
recall a single instance where I received IETF list with a problematic
i travel to places with very poor bandwidth. it is a problem.
and the vast majority of users just do not get it. "we send 20mb
documents around the office all the time. suck it up."
for who has problem in attachment downloading the solution should be
at the delivery Message Store level, where the strip of the attachment could
done accordingly to an user configurable mailbox parameter
(as we do on our server, where we call it Easy Delivery).
Or better still, don't strip anything. Use a reasonably capable client and
that doesn't fetch attachments unless you tell it to.
I'll again note that implementation of this policy will cause people to send
single part messages in order to avoid attachment stripping, which will make it
impossible for clients to avoid downloading material they do not want. In other
words, it will exacerbate, rather than solve, the problem.