[Mimedefang] Rewarding plaintext

[Kenneth Porter]

Given that most of the cost of running a mail server these days is in the spam
and virus checking, it makes sense to penalize messages that facilitate it,
ie. anything non-plaintext, and reward plaintext-only messages.

How might one do this with MD?

One possibility is to throw anything with non-plaintext MIME type into a "slow
boat" queue that gets low-priority AV and spam processing.

Some of us are refusing viruses and egregious spam during the submission. For
those, it might be possible to nice down the AV or SA process once we realize
we're dealing with a non-plaintext part. (This also tarpits the sender, but
that's not the primary objective.) Perhaps the multiplexor needs two pools,
one for plaintext handling and another niced one for the expensive stuff. If
the niced pool is full, we tempfail any new expensive mail.

An advantage of this strategy is that it doesn't make value judgments about
content; it just stratifies delivery performance based on medium type. This
makes it easy for ISP's to deploy and remain content-neutral. It also makes it
easy to explain to end users why they should stop using HTML: It will cost
them a delayed delivery due to its higher processing cost.