Outgoing NAT for Exchange Email
Posted on 2010-11-09
So we got a new internet line here at work to replace our old T1. Along with the new line we were given new IP addresses.
We were given a new WAN IP of xxx.xxx.30.178 /30 which I assigned to the outside interface of the firewall which is a Cisco ASA 5510
We were also given a block of usable public IPs which are xxx.xxx.164.0 - xxx.xxx.164.31 /27
So we made the switchover and everything went fine. But then people in the company started getting all kinds of email bounce backs from people they were trying to send emails to. Apparently this is because our new WAN IP doesn't have a legitimate reverse ARP assigned to it.
Ok no big deal, I call up bellsouth and ask them to do it and they say that our new WAN IP is a Serial IP and that it cannot ever have a reverse arp assigned to it.
The guy at bellsouth told me that we need to configure the firewall in such a way so that the outgoing email looks like it is coming from one of our new Public IPs and not the WAN IP.
So i'm thinking this is going to require some kind of NAT rule, i'm just unsure of how to configure it.
The Internal interface on the ASA is 126.96.36.199 and the Exchange Server is 188.8.131.52.