I have couple of external IP addresses x.x.x.61 and x.x.x.69. I use the x.x.x.69 for NAT. My mail server (192.168.y.20:25) sits behind the firewall and is mapped to the external address x.x.x.61:25. There is no issue with incomming mail. The problem is that when mail is sent out the message appears as comming from x.x.x.69:25 and not from x.x.x.61:25. Some providers (e.g. Comcast) reject the mail based on the fact that the reverse look up does not match.
Is there a way to setup IOS to map outgoing traffic from 192.168.y.20:25 to x.x.x.61:25?