[Mimedefang] Filter on encoding type

[dm at davidmeissner.com]

This is a re-wording of my original question.

Do people see any value in implementing a filter based on invalid encoding types? I 
have observed that there seem to be several bulk mailers that use invalid types; one 
going around right now marks everything with "Content-Transfer-Encoding: plain". 
I'm planning to filter this specific type out, but another option might be to reject 
everything that doesn't match one of the five (six?) valid types. Would such a filter 
reject too much valid mail?

-David Meissner