Red Hat Enterprise Linux 5 and its derivative CentOS 5 includes a graphical tool called Security Level Configuration for configuring the firewall options. This article describes how to use the Security Level Configuration tool to open up the ports necessary for providing an email server.

Firewall Configuration (GUI)

This section describes how to use the Security Level Configuration tool to configure the firewall.

Security Level1. Click System, select Administration and click Security Level and Firewall. This will launch the Security Level Configuration window.
Security Level Configuration2. For a mail server with webmail, check Mail (SMTP), Secure WWW (HTTPS) and WWW (HTTP) in the Trusted services list.
Security Level Configuration
3. We also need to open the ports for the POP3 and IMAP services. In the Other ports field, add the port numbers below.
 
Service
Port
POP3
110:tcp
POP3S
995:tcp
IMAP
143:tcp
IMAPS
993:tcp

Firewall Configuration (TUI)

This section describes how to use the Security Level Configuration text user interface (TUI) tool to configure the firewall.

Security Level ConfigurationLaunch the Security Level Configuration tool using the command below.
system-config-securitylevel-tui
Security Level Configuration2. In Security Level Configuration screen, press the Customize button.
Security Level Configuration3. Open the ports you desire and press OK button when you are done.
 

ImportantYou can see the list of service and port numbers by typing in getent services from the Terminal window.

 

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Posted on 4/23/2007 and last updated on 8/28/2011
Filed under CentOS 5 , Red Hat Enterprise Linux 5 , System Administration