How to Test SMTP Settings Using Telnet

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How to Test SMTP Settings Using Telnet

Article ID: 52275 - Last Review: April 30, 2015


This procedure can be useful when the YourSite Explorer > Mail Servers > Test Mail Server button is returning a failure result, and you need to work out whether this is because of a problem with the settings being entered (as opposed to a problem in the CCM software).


1. This procedure will not allow you to rule out problems that are caused by the mail server selectively screening out emails with Excel documents attached, or alarm emails from Contact Center Client.

2. Additional steps not recorded in this article will be needed to test mail servers which have:

  • TLS (includes
  • SSL
  • Required authentication (that is, mail servers which are not open relay)


Important Note:

When testing SMTP, it is very important to know that you cannot use backspace with SMTP commands.

If you press backspace once you’ve opened a Telnet session to the SMTP port, your cursor will move back and allow you to (seemingly) overwrite what you typed before, but you will get errors and unpredictable results from the command.

Instead, please type carefully, and, if you make a mistake, you may need start over with a new Telnet session.

To test:

1.  In the command prompt, type:    telnet [mail server FQDN or IP] [mail server port]
e.g. telnet 25 , or
    telnet 25

If the command is successful, you will see something like this:

server: 220 ESMTP server ready Tue, 20 Jan 2014 22:33:36 0200
(If the command fails because Telnet is not installed, go to Server Management > Roles and Features > Features, and install the Telnet Client feature.)

2. Carefully, without using backspace, type this:

…where is the name of the computer from which you’re doing the test (i.e. the CCM server)

If the HELO command was successful, you will see this:

3. Carefully type this:
MAIL from:
You should get this reply:
250 Sender Ok

4. Type:
RCPT to:
You should get this reply:
250 Recipient Ok

5. Type:
You should get this reply:
354 Ok Send data ending with <CRLF>.<CRLF>
6. Type this:
Subject: SMTP Test message
Body text goes here - This is a test message.
(The period, all alone on its own line, signals to the SMTP server that you’re done adding body text.)

You should get this reply:
250 Message received:

7. Type:

If you have not gotten an error in this process, the mail server has accepted the message, validating that the mail server settings entered in YSE are valid.


CCM - All versions

port 25 SMTP helo telnet test mail settings mail server

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Last Modified:Thursday, June 04, 2015
Last Modified By: cdoyle
Rated 3 stars based on 3 votes.
Article has been viewed 34,169 times.