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Test SMTP authentication with TELNET

 

Prerequisites:

1)      SMTP server address and port: smtp.example.com:25

2)      Your local hostname. Not crucial at most cases, but better use the DNS name. I’ll use mymailclient.comin this tutorial.

3)      Base64 encoder. Choose the one suits you better:

  1. Online form: http://www.opinionatedgeek.com/dotnet/tools/base64encode/, or any other online form of your choice.
  2. Software like: http://www.slavasoft.com/hashcalc/index.htm, or any other software of form of your choice.

4)      Login details encoded in base 64:

  1. Username: user@example.com -> encoded in base64: dXNlckBleGFtcGxlLmNvbQ==
  2. Password: XXXXX -> encoded in base64: YWJjMTIz

The session:

                Basically all you need is to open a telnet conection to the right server on the right port. The following example is totally forged. NO REAL DATA USED!!!!

Q: C:\>telnet smtp.example.com 25

A: Connected to smtp.example.com (1.1.1.1).

A: Escape character is '^]'.

A: 220- smtp.example.com ESMTP Exim 4.66 #1 Wed, 09 May 2007 23:55:12 +0200

A: 220-We do not authorize the use of this system to transport unsolicited,

A: 220 and/or bulk e-mail.

Q: EHLO mymailclient.com

_________

If you are testing a server that doesn’t require AUTH do:

Q: HELO mymailclient.com

And continue to Section 2

_________

A: 250-server1.exampledomain.com Hello  [1.1.1.2]

A: 250-SIZE 52428800

A: 250-PIPELINING

A: 250-AUTH PLAIN LOGIN

A: 250-STARTTLS

A: 250 HELP

Q: AUTH LOGIN

A: 334 VXNlcm5hb3WU6

Q: dXNlckBleGFtcGx2lLmNvbQ==

This is your base64 encoded username

A: 334 UGFzc3dvcmQ^6

Q: YWJjMTIz

                This is your base64 encoded password

A: 235 Authentication succeeded

 

Section 2: Sending the Email

                If you got here by passing the austhentication just continue the command in same session.

 

Q: MAIL FROM: test@test.com

A: 250 MAIL FROM accepted

Q: RCPT TO: test@test.com

A: 250 RCPT TO accepted

Q: DATA

A: 354 continue.  finished with "\r\n.\r\n"

Q: Cc: test@test.com

Subject: Testing SMTP auth by telnet.

 

Hello,

Do not reply.

.

A: 250 OK TrackingID:5e14523646-8dab-42dd-b2cc-5a20413ed295

 

Congratulations, you just sent an email using telnet!

 

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