SOLVED: Quick Way To Test A Mail Server Using Telnet

If you have a mail server that you are having problems with, the easiest way to test it is using Telnet:

1. Launch APPS AND FEATURES
2. Install TELNET
   1. Windows 10 –  PROGRAMS AND FEATURES > TURN WINDOWS FEATURES ON OR OFF
   2. Windows 2016 – SERVER MANAGER > LOCAL SERVER > MANAGE > ADD ROLES AND FEATURES > Telnet is a FEATURE
3. Launch CMD
   • always a good idea to RUN AS AN ADMIN, but not required
4. Type TELNET <MAIL.DOMAIN.COM> 25 and press the enter key
   • this is not case sensitive
   • obviously, substitute your mail server in the <>

If it fails you will likely see Could not open connection to the host, on port 25: Connect failed

• If you have access to the mail server you can check the firewall to make sure port 25 is open
• You should then ping the mail server to see if your DNS has the correct IP entry for it
• You can also try to TRACERT to that mail server to see where it is failing