unable to open the smtp port

[jawad]

why is it unable to connect to the smtp, pop3 and imap4 port, how can i figure it out?

[Code Crafters]

This error indicates that another mail server is already running on that computer and is using the needed ports. Only one application can use a port for each available IP.

The easiest solution is to disable or uninstall all other mail servers running. The most common of these is usually Microsoft IIS mail server which can be disabled via Control Panel -> Administrative Tools -> IIS but this only uses SMTP and POP3 generally so it's probably another mail server in your case.

You can open a command prompt on the mail server computer (Run: cmd) and type "telnet localhost 25" to connect to port 25 (SMTP) and get a welcome message back to see what software is running there. Obviously, you can do this for the other ports too.