I've been struggling with this on and off for quite a while now. In january we were purchased by another company and were converted to be a part of their domain. We have our own domain within their forest.
We were doing just fine until we came across an email address that we kept on getting non-deliverable messages back from. None of our emails go through. This company that I work for is actually two in one, both companies have different mail.domainname.com address but we both go out through one internet connection. We've tried sending emails from email address from both companies (both companies have different @domainname.com addresses).
According to www.dnsstuff.com
we are on that fivetensrc blacklist because we have no reverse DNS set up for our outgoing IP (68.x.x.x). Both of our mail.domainname.com addresses have a reverse dns set up to go through our parent company's ip address (65.x.x.x) because our incoming mail goes through their filtering system. But our outgoing mail goes out directly through our outgoing IP. Our ISP and our parents' ISP are different. I tried talking to a couple people and what I understand is that if i change our mail.domainname.com's reverse DNS to our outgoing IP (68.x.x.x) then we will resolve that blacklist issue but we won't be going through our parent company's spam filter (I want our incoming email to go through their filter) or their exchange server (They want us to go through their server for incoming mail so that they can watch and filter things etc).
The people in the DNS department of my ISP seem to think that you can't set up one ip address to have a reverse DNS to multiple domain names. Which doesn't make sense because the reverse dns of all 3 of our mail servers domain names - our two and our parents one all resolve to the same address (65.x.x.x). Also, they say that they can't set up one IP to reverse to multiple domain names - even though both of our domains are going out the same connection.
Oh, by the way, we're running 1 domain controller thats on server 2003, 1 exchange server - exchange 2003
our parent company im not sure what all they have but im certain they are using exchange 2003 and server 2003