I have a Cisco ASA 5505 with security plus licensing, an Exchange Server and internet connections.
Here is what I need. The "outside" interface is connected to my DSL modem and has an IP address of 1.1.1.1. I want to use this DSL connection for web browsing.
The "inside" interface has an IP address of 192.168.0.3, my email server has an IP address of 192.168.0.246 and is connected to the inside interface by a switch.
The "public" interface has an IP address of 2.2.2.2. This is the IP address I want people outside of my network to use to access my email server. When users try to access my email server their traffic will be addressed to 2.2.2.2. When the traffic reaches the firewall there will be an access-list to allow the traffic in. There will then be a static rule to translate/route/direct the traffic to the email server at 192.168.0.246. When responding, the email server send the responding traffic out the "public" interface.
I am doing this right now on a Sonicwall 2040.