Telnet and CMD not recognizing commands

Jamie King
Jamie King used Ask the Experts™
I've been trying to use telnet to send emails, but commands like MAIL TO are described as unrecognized. Any solutions?
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Dr. KlahnPrincipal Software Engineer

It is increasingly difficult to use Telnet to check anything except the simplest SMTP connections, because most sites use extensions, firewalls, context filtering and IP-based filtering to restrict spam.  SMTP connections must therefore be exact and precise, be quick with timing and responses, and conform to what the receiving MTA considers valid.

An example of the last can be found at Microsoft's web site regarding SMTP to Exchange MTAs.  The exchange is close to, but not quite "usual" SMTP, particularly as regards AUTH LOGIN and the encrypted usernames.

If you can show us a session log, it will be helpful.


As per Dr Klahn, please can you post a copy of the interaction.

I am assuming you are successfully submitting a HELO / EHLO, and getting a valid response?


System Administrator / Postmaster
Moreover, MAIL TO is correctly not recognized - use MAIL FROM and RCPT TO and  look for SMTP verbs in the pages linked above.
Jose Gabriel Ortega CastroTop Rated Freelancer on MS Technologies
Awarded 2018
Distinguished Expert 2018

This is one of my "go to" forums when trying to do testing with Telnet (mostly for exchange server)

telnet 25
220 Microsoft ESMTP MAIL Service, Version: 5.0.2195.5329 ready at Sun, 15
Sep 2002 23:51:06 +0200
250 Hello []
mail from:
250 2.1.0 OK
rcpt to:
250 2.1.5
354 Start mail input; end with .
subject: this is a test
Hi Daniel
I'm trying to test this connection from Telnet.
Let me know if you get this message.
250 2.6.0  Queued mail for delivery
221 2.0.0 Service closing transmission channel
Connection to host lost.
Press any key to continue...

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The point in here is that "mail to" doesn't exist it would be "rcpt to" and "mail from"

Michaelangelo identified the issue.

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