PTR record

I am setting up a new email server. I have a test domain setup with an mx record. I can send email to most domains, but when i try to send to aol my mail gets bounced, because i have not ptr record to do reverse dns. The ip address of the current domain we have is in the same ip block from our isp, and also has no ptr. We do have our mail filtered through postini, and the mx points to their server before ours. Could this explain why we can now send mail to aol? anyone have any other ideas? Any help would be great.

Thanks.