I have a Cisco 1811 Intergrated Services Router which has been in operation for over a year. It also provides VPN access for the Cisco dialer VPN and three small remote offices with PIX 501s connected back to the main office. All worked well, except I discovered the outbound e-mail came from an incorrect IP address. I want the SMTP to show from 126.96.36.199, but it shows from 188.8.131.52. 192.168.10.111 is the e-mail server. I used the command "ip nat inside source static tcp 192.168.10.111 25 184.108.40.206 25 extendable". E-mail comes in OK, but outbound e-mail shows the primary IP address of the router, not the address in the IP NAT line. The server is also a DNS/WINS server. I do not want to change the public DNS records. I have tried some changes, but each try created a different problem.
Attached is a copy of the full config.