Cisco 761M connecting to ISP using public ip

[Ajiemher]

Hello,   One customer of ours will be using cisco 761M router to connect to the internet. They have a registered domain name and a set of public ip address.  They also plan of having their own mail server using Exchange Server 5.5. My questions are as follows:   1. What is the best approach to this solution? Should i use PAT or just use public address to all host in the private network? 2. If i use PAT, how will i let my exchange server receive and send mail if its ip address is a private one? Is there a way to     map private ip address to public ip addres  under cisco 700 series router? 3. If i use public ip address to the hosts in the network including the exchange server, how will I secure the network from outside     world? The SET IP FILTER command for cisco 700 series router in the cisco web site is not clear enough for me.   I have no problem with exchange server since i've have done such work of connecting exchange server to the internet. This is my first work that involves cisco router.   I will appreciate any help from you guys....   Thanks in advance...   itsme,   Ajie of Dubai CCNA