How to Test an SMTP Server Using Telnet

Simple Mail Transfer Protocol, or SMTP, is one of many email protocols used by email servers.

Before the days of free internet email accounts, users employed Telnet and a command line to access their email. Telnet was developed in 1980 by a company named Postel as a means to allow computers to communicate with each other. Simple Mail Text Protocol, or SMTP, was developed not long after telnet as a standard for sending email across Internet Protocol. You can test an SMTP server using Telnet through a series of mail-related greeting commands that request basic data on the SMTP server. After each command, Telnet provides feedback as to the success or failure of the command.

Things You'll Need

• Telnet
• Server domain name
• SMTP server port

Instructions

1. Click "Start" from the Windows operating system.

2. In the search field, type "cmd". A command prompt window opens.

3. Type "Telnet."

4. Type "open <servername><portnumber>". For example, if your server name is mailyouroffice.com and your port is 25, you would type: "open mail.youroffice.com 25."

5. Press "Enter." You should see a response that indicates the SMTP mail service is ready at the current moment.

6. Type "EHLO <servername>" and then press enter. Using myoffice.com as the server name you would type: "EHLO myoffice.com."

7. Press "Enter." You should see a response that says Hello <your IP address or server name>. This indicates success.

8. Type "MAIL FROM: <youremailaddress>." Press "Enter." You should see a response that states "Sender OK."

9. Type "RCPT TO: <recipientaddress> NOTIFY=success, failure." Press "Enter." You should see a response that indicates "Recipient OK."

10. Type "DATA." Press "Enter." There is no confirmation from Telnet as to the success of this step.

11. Type "Subject: Test." This step is optional. Press "Enter." There is no confirmation from Telnet as to the success of this step.

12. Type: 'This is a test." Press "Enter." There is no confirmation from Telnet as to the success of this step.

13. Type "."

Tips & Warnings

• You cannot delete text with backspace in Telnet. If you incorrectly enter a command, press enter and enter the command again.

• Always use a valid sender address and domain.

References

• Microsoft Technet: Using Telnet to Test SMTP Communication
• History of Telnet

Resources

• Microsoft Technet: Install Telnet Client
• Microsoft Technet: Using Telnet to Test SMTP Communication