How can I check if port 25 is open?

If you know the mail server is up and running, check whether you can talk over port 25 to your mail server. This can be done using a one-line command: telnet <appserver name> 25 Substitute the <appserver name> with your own server.

Once you type this into your DOS window and hit return, you should see some sort of response from your mail server, as shown below:

Trying Connected to ( Escape character is '^]'. 220 SMTP Server (JAMES SMTP Server 2.2.0) ready Mon, 27 Jul 2009 06:38:20 -0700 (PDT)