Standard Internet Ports  

You can find a list of port numbers on the Internet. The list will specify the port used by a server process (or program) as its contact port. Standard (well-known) ports range from 1 to 1022. A non-standard port is a port whose number is higher than 1023.

For example

Your email program uses a mail server (server process) to send and receive mail. Simple Mail Transfer Protocol (SMTP) is used to send email messages via Port 25. Post Office Protocol (POP) is then used to retrieve the emails via Port 109 or Port 110. This is why eBlaster listens at Ports 25, 109 and 110 to record email.