[exim] Question: How to block HTML-only emails with exim?

Hello all,

First I would like to say thank you to all those people contributing to the
development of the exim MTA. I've been using exim for years now.
Nevertheless I've subscribed to this list now because I've a question I was
unable to find an answer to during my searches:

I would like our exim mail server to block any incoming emails
which only have one or more HTML attachment(s) and don't
contain at least one plain text attachment.

Is this possible and how can I configure exim to act like this?

Yesterday I've asked the same question on the net here:
http://serverfault.com/q/750777/163536 but got only down votes.

Best Regards,
Peter Funk
--
Peter Funk, home: ✉Oldenburger Str.86, D-27777 Ganderkesee
mobile:+49-179-640-8878 phone:+49-421-20419-0 <http://www.artcom-gmbh.de/>
office: ArtCom GmbH, ✉Haferwende 2, D-28357 Bremen, Germany