Network adjustment for Messaging gateway

hi everyone,

please enlight me with setup of 1 SMG 8340 (inbound and oubtound filtering), what are the network adjustment needed specially in firewall;

we plan the SMG will be install behind firewall. Please see detail below if the configuration are correct?

a.1 private each for (inbound and outbound) and 1 public Ip---  Do i request to firewall admin to create NAT 1 public address to 2 private IP address?

b. Mx- 10 for SMG, Mx 20- lotus domino server

c. create/adjsut  DNS server for 2 ip address of SMG (inbound and outbound)- A and PTR record

d. point all outbound mail from lotus Domino mailserver to SMG appliance outbound IP address.

Please correct me if miss something or wrong setup.

thank you all