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How to Use Telnet to Test SMTP Communication
Topic Last Modified: 2005-05-24
Telnet is an extremely useful tool for troubleshooting issues related to SMTP and mail flow. For example, you can use telnet to:
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Verify that SMTP is installed properly, and that it has all the necessary commands.
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Ensure that your server is accessible over the Internet.
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Attempt mail delivery directly over the TCP port.
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Determine that all servers are accepting connections.
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Determine if a firewall is blocking a connection.
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Ensure that a single user can receive mail.
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Ensure that a specific domain can receive mail.
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Ensure that a specific user or domain can send mail to your domain.
 Note: |
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| The following procedure shows you how to test the process of an internal user sending mail to a remote user when basic authentication is required for relaying mail outside your organization. |
Before you perform the procedure in this topic, read Troubleshooting Mail Flow and SMTP.
The following permissions are required to perform this procedure:
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Member of the local administrators group
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Open a telnet session: From a command prompt, type telnet, and then press ENTER.
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Type set local_echo on a computer running Microsoft Windows® 2000 Server or SET LOCALECHO on a computer running Windows Server™ 2003 or Windows XP, and then press ENTER. This command allows you to view the responses to the commands.
Note: For a list of available telnet commands, type set ?. -
Type o <your mail server domain> 25,and then press ENTER.
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Type EHLO <your mail server domain>, and then press ENTER.
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Type AUTH LOGIN. The server responds with an encrypted prompt for your user name.
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Enter your user name encrypted in base 64. You can use one of several tools that are available to encode your user name.
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The server responds with an encrypted base 64 prompt for your password. Enter your password encrypted in base 64.
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Type MAIL FROM:<sender@domain.com>, and then press ENTER. If the sender is not permitted to send mail, the SMTP server returns an error.
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Type RCPT TO:<recipient@remotedomain.com>,and then press ENTER.If the recipient is not a valid recipient or the server does not accept mail for this domain, the SMTP server returns an error.
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Type DATA.
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If desired, type message text, press ENTER, type a period (.), and then press ENTER again.
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If mail is working properly, you should see a response similar to the following indicating that mail is queued for delivery:
250 2.6.0 <INET-IMC-01UWr81nn9000fbad8@mail1.contoso.com.
The following example shows a telnet test sending mail from contoso.com to a remote domain with a successful result:
250-mail1.fourthcoffee.com Hello [172.16.0.0]
250-TURN
250-ATRN
250-SIZE 5242880
250-ETRN
250-PIPELINING
250-DSN
250-ENHANCEDSTATUSCODES
250-8bitmime
250-BINARYMIME
250-CHUNKING
250-VRFY
250-X-EXPS GSSAPI NTLM
250-AUTH GSSAPI NTLM
250-X-LINK2STATE
250-XEXCH50
250 OK
334 VXNlcm5hbWU6
334 UGFzc3dvcmQ6
235 2.7.0 Authentication successful.
250 2.1.0 kim@fourthcoffee.com....Sender OK
250 2.1.5 ted@contoso.com
354 Start mail input; end with <CRLF>.<CRLF>
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250 2.6.0 <INET-IMC-01UWr81nn9000fbad8@mail1.fourthcoffee.com> Queued mail for delivery
For more information, see Securing Your Exchange Server.
