Red Hat Enterprise Linux 4 and its derivative CentOS 4 includes a graphical tool called Security Level Configuration for configuring the firewall options. This guide describes how to use this tool to open up the ports necessary for providing an email server.

Security Level1. Click Applications, select System Settings and click Security Level. This will launch the Security Level Configuration window.
Security Level Configuration2. For a mail server with webmail, check WWW (HTTP) and Mail (SMTP) in the Trusted services list. There are only four predefined trusted services, the other services will have to be entered into the Other ports field.
Security Level Configuration
3. We also need to open the ports for the POP3 and IMAP services. In the Other ports field, type in 110:tcp,995:tcp,143:tcp,993:tcp. The service and its corresponding port number is provided below.
 
Service
Port
HTTPS
443:tcp
POP3
110:tcp
POP3S
995:tcp
IMAP
143:tcp
IMAPS
993:tcp
 
Port 443:tcp is automatically added if you check the WWW (HTTP) service.

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

 

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Posted on 3/19/2007 and last updated on 11/7/2009
Filed under CentOS 4 , Red Hat Enterprise Linux 4 , System Administration