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When I pinged my mailserver from the command prompt using:

telnet 25

I got the error Telnet is not a recognized command. I looked for a workaround and then found that Telnet was unchecked by default in Windows. Once i checked it, it started working.

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I don't know the exact answer, but I heard it was something to do with security. – Sasha Chedygov Feb 19 '10 at 6:20
up vote 17 down vote accepted

TELNET communicates with the peer (telnet server) in clear text.
This is a security hazard compared to say the SSH connect. To this end, the telnet client on windows is disabled by default. This often comes as a surprise and many sites describe the steps to get it working,
you seem to have found them already :)

For normal purposes, it would be a better option to use SSH (PuTTY or freeSSHd if you want to connect to a Windows machine).

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My favorite part is that they disabled telnet and didn't give me ssh. D: – Rob Oct 21 '11 at 15:31

When wanting to query in clear text an SMTP server, to my knowledge, there isn't any simpler way to do it than Telnet. [SSH can't be used for this]

In this case I advise you to enable telnet or to use something like SMTPDiag.

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@simtris, I appreciate the ease of working with TELNET to talk with an SMTP server. I also agree that enabling TELNET is a good idea to connect with the SMTP server as the OP wants to. I see the question as a query on the reasons for something as simple as the telnet client needing to be enabled. Do you see a different question or think my answer deviates from the point in discussion? – nik Feb 19 '10 at 11:53
@nik : U right, his question was about the "disapearance" of the telnet client. You anwer the part "security", I addead the part "usefull" :) – user26604 Feb 21 '10 at 10:50
@simtris, fair enough :) – nik Feb 21 '10 at 13:20
Since this question was referenced recently by answers to other questions, I have edited this answer to remove commentary on other answers (it's author lacked rep to make comments at the time). – RedGrittyBrick Oct 21 '11 at 15:30

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