[Exim] Reverse Mappings

Hello list;
For the past several months now, I've been denying hosts with no reverse
mapping on their IP's, and believe me, this stops
a lot of spam! But, I've also been watching how many legitimate hosts are
being denied, because their admins, or themselves
do not have correct reverse mapping set on their IP's.
Now, I know the world is perfect, and mistakes are made, but I would think
that any professional mail server would have both
forward and reverse lookups functioning on it.
I recently disabled that check, since a few signifigant e-mails have been
unfairly dropped, but I would just like to ask a question to
everyone here; how many legitimate mail servers do you guys think there are
running out there without correct reverse lookups?

I'm just curious, because it has stopped a lot of those up one day, down the
next mail servers who send 5 million e-mails, and go
down immidiatly after that, but like I said, a few messages that were
legitimate were also dropped.
Thanks guys!

Brent Jones
brentj@???