Duplicate mails

Hi All

We installed a new Mail Gateway for our Lotus Domino mail server for
spam controlling, using following software,

	exim4 - 4.50-4
	sa-exim - 4.2-2
	spamassassin - 3.0.2-1
	Debian - Sarge

It simply scan all the in-coming mails and forward it to Domino server
to delivery. It's working fine except a small problem.

Problem is, after we place this gateway, we are getting duplicate emails
from certain domains (most of the domains are ok). Specially from
gmail.com and few of our customers. What could be the problem? Or where
should I look in to?

Thanks!

Pradeeper