Redhat / CentOS / Fedora Linux Open Port

Open flle /etc/sysconfig/iptables:
# vi /etc/sysconfig/iptables

Append rule as follows:
-A RH-Firewall-1-INPUT -m state --state NEW -m tcp -p tcp --dport 80 -j ACCEPT

Save and close the file. Restart iptables:
# /etc/init.d/iptables restart

 Open port 110

Append rule as follows:
-A RH-Firewall-1-INPUT -m state --state NEW -m tcp -p tcp --dport 110 -j ACCEPT

Open port 143

Append rule as follows:
-A RH-Firewall-1-INPUT -m state --state NEW -m tcp -p tcp --dport 143 -j ACCEPT

 Restart iptables service

Type the following command:
# service iptables restart

Verify that port is open

Run following command:
netstat -tulpn | less