Sonicwall NAT Policy + Firewall Rules needed to forward SMTP traffic to Exchange 2007 mail server

First, you need to create 2 Address Objects. one which corresponds to the public IP of the Exchange 2007 server and one that corresponds to the private IP.

For NAT policy, you have to add 2 rules that are mirror images of one another.  Go to the WAN > LAN area.  Add first NAT policy:

Source Original = Any
Translated = Original
Destination Original = Public IP address object
Translated = Private IP address object
Service Original = SMTP
Translated = Original
Interface Inbound = WAN IP (X1 interface)
Outbound = Any

Add second NAT policy:

Source Original = Private IP address object
Translated = Private IP address object
Destination Original = Any
Translated = Original
Service Original = Any
Translated = Original
Interface Inbound = LAN IP (X0 interface)
Outbound = WAN IP (X1 interface)

Then you need to add a firewall access rule:

Source = Any
Destination = Public IP
Service = SMTP
Action = Allow
Users = All

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