Let me start with the fact that things are quite weird in our organization.
Now, we have to place a mailserver for a DNS zone that is under our control, for example
xxx.yyy.zzz. However, we can't place it physically in the subnet allocated for this zone.
At the current moment we have two possibilities. Place it in a different subnet with it's own DNS zone and insert it into the rDNS for that zone. That is, our DNS points at that IP, their rDNS points at our domain name.
Alternatively, we can place it in a different subnet and rDNS lookup won't work.
My question here is, is either of these setting "mail-friendly". That is, will mail servers, mail clients, spam detection, etc. tolerate such a setting or there is a great chance e-mails from such a server will be dropped, marked as spam and so on.