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Jamie King asked on

Telnet and CMD not recognizing commands

I've been trying to use telnet to send emails, but commands like MAIL TO are described as unrecognized. Any solutions?
Windows OS

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8/22/2022 - Mon
Dr. Klahn

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?



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Jose Gabriel Ortega Castro

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


telnet srv1.dpetri.net 25
220 srv1.dpetri.net Microsoft ESMTP MAIL Service, Version: 5.0.2195.5329 ready at Sun, 15
Sep 2002 23:51:06 +0200
helo srv1.dpetri.net
250 srv1.dpetri.net Hello []
mail from: admin@petri.com
250 2.1.0 admin@petri.com....Sender OK
rcpt to: danielp@dpetri.net
250 2.1.5 danielp@dpetri.net
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 srv1.dpetri.net 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"
I started with Experts Exchange in 2004 and it's been a mainstay of my professional computing life since. It helped me launch a career as a programmer / Oracle data analyst
William Peck

Michaelangelo identified the issue.