Concepts of [nolisting](http://nolisting.org) and [greylisting](http://projects.puremagic.com/greylisting/) should be known.

Imagine this setup:

~~~
example.org         IN  MX  05 192.0.2.5
example.org         IN  MX  50 192.0.2.50
example.org         IN  MX  99 192.0.2.99
~~~

All addresses are on the same host running exim.
Exim would go through the whole process (almost – since most stuff is rejected anyway, one may want to optimize here) as normal, but will `tempreject` (almost – abuse@ and postmaster@ should probably be unfiltered, just to make sure) everything on 192.0.2.5 and 192.0.2.99.

Is anything wrong about this (WRT to RFCs)?
What might go wrong?