Locals Only Postfix
The default Rhel5 Postfix installation does not have an interface assigned for use. This is similar to the default Rhel5 Sendmail defaulting to only serve localhost.
To over come this behavior, you can use the Postfix installed postconf utility as opposed to a direct edit to the file ’/etc/postfix/main.cf’
postconf -e "inet_interfaces=all"
Next issue either ‘postfix reload’ or ‘service postfix restart| stop | start’ as root.