Exchange e-mail exiting my network from wrong IP address

Alright, so we have an external IP block for our mail server and a few other machines, and we have a WAN interface ip.

Previously, our mail server traffic would be routed out of its own IP address to the internet. All of a sudden, our mail server traffic is instead being routed out of our WAN ip which has no reverse DNS. This is causing me major headaches getting mail through to AOL, Comcast, and a few other domains. I haven't altered the configuration of our cisco 2811 router/firewall in months and I'm not sure what would be causing this change. The nat statement for our mail server is such:

ip nat inside source static 192.168.0.9 65.121.x.x

Any ideas?

From serverfault wooz

• Never would the source IP appear as the internal from outside the network. Did the mail server NAT through a different external IP than it is now using?

  wooz : Some yoyo appears to have un-teamed my two nics, one of them grabbed a different internal IP via dhcp and it chose to use that one to communicate. Re-teamed the cards and told exchange to always use its .9 internal address.
  From MisterITGuy