Reference guide to basic Telnet Commands

Occasionally you might need to test a mail server manually using Telnet and SMTP commands.

Before running Telnet you might need to install it (Microsoft Windows 7 and above) by following either three of the following steps:

By Command Prompt

  1. Open a command prompt
  2. type “appwiz”
  3. Click on “Turn Windows features on or off”
  4. Click on “Telnet Client” and click OK

By Windows

  1. Open Control Panel
  2. If view by “Category” Click on “Get Programs” under “Programs”
  3. If view by “Small icons” Click on “Programs and Features”
  4. Click on “Telnet Client” and click OK

Other Versions of Windows

This is great for troubleshooting a SMTP mail server as the process of sending an email can come up with errors along the way that a fat mail client might hide from you.

HELO <hostname>    =          This command initiates the SMTP conversation. The host connecting to the remote SMTP server identifies itself by its fully qualified domain name.

EHLO                          =          An alternative command for starting the conversation. This states that he sending server wants to use the extended SMTP (ESMTP) protocol.

MAIL FROM:              =          This is the start of an email message. The source email address is what will appear in the “from” field of the message

RCPT TO:                   =          This identifies the recipient of the email message. This command can be repeated multiple times for a given message in order to deliver a single message to multiple recipients.

DATA                          =          This command signifies that a stream of data, i.e the email message body will follow. The stream of data is terminated by a “.” on a line by itself.

“.”                                 =          To end the body of the message, type a full stop on a single line by itself.

QUIT                           =          Quits out of the Telnet session


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