Some time local ISP blocked default SMTP port 25 in the local network therefore we have to configure the alternative smtp port for SMTP service, so that SMTP will work on default port 25 as well as other new port. For example we are configuring the SMTP service on port 2626. Refer to the following steps to configure SMTP service on another port.
Change directory to the /etc/xinetd.d
root@server [~]#cd /etc/xinetd.d
Now copy the current working smtp_psa file to the new file smtp_psa_new
root@server [/etc/xinetd.d]#cp -p smtp_psa smtp_psa_new
open the file smtp_psa_new and change the value in the first line
From
service smtp
to
service smtp_psa_new
Save the file and add the new smpt port in the /etc/services file
For example we want to set new smtp port 2626, you can change the port as per your requirement
smtp_psa_new 2626/tcp mail
smtp_psa_new 2626/udp mail
Save the file and restart the xinetd service
root@server [/etc/xinetd.d]#/etc/init.d/xinetd restart
Make sure that you have opened new port in the server firewall and then try to telenet the new SMTP port
root@server [/etc/xinetd.d]#telnet localhost 2626
It will show you the SMTP service banner
