i'm assuming you are negotiating your address on dialer 0. are you going to readdress you internal network? right now your are forwarding smtp traffic that hits dialer1 to 10.0.0.201. if you add a fw it is going to have to have an internal interface and an external inteface unless it is one that supports a "drop-in" mode where it actually acts like a bridge. If no drop-in mode, you could put a static nat entry on the fw for 10.0.0.201 ext for smtp and map it to the new ip address of the internal mail server. Thats actually the easy part, there is probably a statement that looks like ip nat inside source list (or routemap) interface dialer0 overload. That is for all outbound traffic. But I guess you could just do nat twice, the firewall would nat all to the outside address of the fw, i.e. 10.0.0.1 and then the router would get it on lets say 10.0.0.2 on fa0/0 and forward it out dialer1 and nat it to the negotiated interface of dailer1. A little cludgy, but would work. The other iption would be to get a range of ip address from your isp and put them on the network between the fw and the router. By the way are you using dynamic dns of some sort or I guess you could have a static ip on dialer1.
