Number of Public IPs needed for SMG

Dears,

Good Day !

im currently in the process of installing SMG appliance, and i want to make sure wether i can use 1 public IP for SMG (for Inbound / Outbound mail flow) while using a second public IP for owa on Exchange.

I've read on the SMG guide that i can use 1 public IP for inbound and outbound, by configuring different ports.. but didnt really get that part..

Is it like configuring inbound mail on port 25 on the firewall and configure outbound mail on port 30 for example??

Appreciate your help..

regards,

Omar