We have multiple domains that we want to send email from. This means that we need to be able to have Reverse DNS set up for each of these domains to email delivered to some recipients (i.e. at AOL). My current understanding is that I need to have a unique IP address for each domain for reverse DNS to work (that's what our ISP has told us).
Right now we support about 30 domains on a single server computer. Probably we will only have about 5-6 domains that we will want to send email from.
We have a range of IP addresses from our ISP. (As I write this, it occurs to me to wonder whether we just need to have the PTR record set by our ISP to make AOL happy, or do they actually check what is going on at the IP address?) However, how do we set it up so that we can have our single server handle multiple IP addresses? (Our ISP said something about getting a router with virtual ports).