FAQ about forwarded mail?

I've searched the sa-exim list archives and I've seen this issue brought
up a few times, but never with what seemed to me to be a definitive
clear answer about how to properly set up a system to handle forwarded
mail.

Forwarded mail is different from non-forwarded mail since rejecting
such messages is likely to produce collateral damage, and grey listing
such messages is actually counter-productive.

Is there a simple guide to configuring sa-exim to never bounce or
greylist forwarded mail?

Eric