Question : should the reverse dns lookup reference the sending exchange server or the forwarding receiver?

i have two clients - one on sbs 2000 and one on exchange 2003 - having an outside agent receive their mail and forwarding it to them once it's been "cleaned".  

they are getting returns from the likes of comcast, aol, time warner and bell south.  they are not on any spam lists and when contact any of the companies, they show my customers' domains as not being blocked.  however both are having similar issues and i believe it's tied into the reverse dns lookup.

if i ping the mail.servername.com it returns the address of the receiver/forwarder and if i do a reverse dns lookup on that ip address it returns the mail.servername.com of my client.  they are on two different services so it's not an issue on their end.

so my question is - should the reverse dns lookup really be pointing to the actual exchange server sending the email?

Answer : should the reverse dns lookup reference the sending exchange server or the forwarding receiver?

Yes - the reverse DNS of the IP address needs to be the server sending the mail as this is exactly what the reverse lookup is checking - that the sender server is from the organization