How to test if a port is open on a server or PC

Further info to my previous post on How to access web page without using web browser, you may use the same method to confirm if a network service is running on a server or computer.

For example if you like to test if pop3 is running on a computer PC1, you may execute the following command in your terminal:

telnet PC1 110

where PC1 can be the hostname of PC1 or IP address of PC1, and "110" in this case is the port number used in POP3 protocol.

Similarly if you like to test if mail service is running on a server, you may try:

telnet PC1 25

where port 25 is the port number use in SMTP (Simple Mail Transfer Protocol).