Using TELNET to Troubleshoot Email Connectivity Issues in

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Telnet is a useful tool to use when troubleshooting email connectivity issue with It's a network protocol that allows a user to log in to a remote computer.

Using a telnet connection, you can troubleshoot connectivity issues between an email server and an email client ( Unsuccessful telnet connections indicate either a firewall or other connectivity issues.

For the purposes of troubleshooting email in, telnet is a tool that is used to check to see if ports are either opened properly, or returning errors on your mail server.

How to use Telnet to troubleshoot email connectivity issues in

For Windows, go to Start > RunCMD
For Macs, go to Finder > Applications > Utilities > Terminal

At the command prompt, type telnet:

The return response should look like this:

At the telnet prompt, type in the following information (open [incoming serverport) like in the following example below: (Notice the space after open and before the port)

You would see a good result that looks like this:

You can use the telnet tool to troubleshoot connectivity issues on any port. Specifically for email, you can use it to troubleshoot issues on IMAP (143, 993), SMTP (25, 587) or TLS (465). You would just change the port number in the OPEN command.

open 143
open 993
open 25
open 587
open 465

You can do far more advanced troubleshooting for email using telnet. Please refer to the article here on how to check the full sending process using telnet.