Did you create firewallrules to allow the incoming traffic? Only 1:1 NAT is not automatically passing all traffic (which would be a bad idea anyway).
Let's say one of your IPs is a webserver for example you need a pass rule like this:
protocol tcp
source IP any
sourceport any
destination IP <lan-ip of="" mailserver="">(NAT comes first, then firewallrules are applied so you have to use the internal IP as destination)
destinationport http (80)</lan-ip>