When I m chcking running port by using
nmap -sT -O localhost
command i m geting following port rtunning
21/tcp open ftp
22/tcp open ssh
23/tcp open telnet
25/tcp open smtp
80/tcp open http
111/tcp open rpcbind
113/tcp open auth
143/tcp open imap
631/tcp open ipp
993/tcp open imaps
3306/tcp open mysql
8009/tcp open ajp13
Device type: general purpose

I want to start POP3 ie 110 port.

any one ccan help me to start pop3 ie 110 port.

command line or GUI?

I got my solution.
we can open port 110 by starting pop3 server using following command.

/etc/init.d/dovecot start

but it was giving me error stating
chkconfig: command not found

linux 2.6.9-5.ELsmp #1 SMP Wed Jan 5 19:30:39 EST 2005 i686 i686 i386 GNU/Linux

looks like RHEL, so chkconfig should work

try system-config-services, and add the pop3 daemon to automatically startup in there

system-config-security or system-config-firewall may also help