An easy method to do port forwarding without the iptables is to use the xinetd.
In order to port forward with xinetd, you will need to create a configuration file:
root# vim /etc/xinetd.d/imap_forward
For example: Forward port 143 on localhost to remote server on port 143:
service imap_forward
{
disable = no
type = UNLISTED
socket_type = stream
protocol = tcp
user = nobody
wait = no
redirect = remote_IP_or_server_name 143
port = 143
}