Here is the basic document which describes boiler plate security configurations that should be considered on every perimter router.
Improving Security on Cisco Routers
http://www.cisco.com/warp/customer/707/21.html
Here are some configuration examples for the IOS F/W feature set, including NAT, RFC 2267 filtering, etc.
IOS Firewall
http://www.cisco.com/warp/customer/707/#IOS
Don't know what you mean by SMTP forwarding, but I'm guessing that you mean a static NAT that will hide your mail server's internal address. That is covered in basic NAT configurations also.
HTH
Jeff