When a consultant set up a firewall and exchange email server for me, they told me to have my ISP set up a reverse DNS lookup for my email server. I am in the process of switching ISPs and reconfiguring the firewall.

Can I have my new ISP set up a new reverse lookup for the new IP address of my email server, while the other still exisits?

In other works can I have two reverse lookups (IP addresses) pointing to the same name (ex. mail.mydomain.com)?