[Exim] Refusing mail because of missing MX record

There was some discussion about that on another forum.
Any pros or cons ??

Idea was that if sending server does not have valid MX record
it is so badly administered that it is propably sending spam
as well (and their users have lice and bad breath) :)

Is there way to do that on Exim ?
By reading the docs, mx_domain affects sending only.

Cheers
--
lauri.tischler@???