DevNull SMTP: A dummy SMTP server for testing and troubleshooting

Microsoft Exchange administrators are often drafted into the service of trying to debug connectivity problems between local or remote SMTP servers. SMTP can be complicated and capricious to troubleshoot, so the more details you can have available, the better.

One of the more interesting SMTP tools I've come across lately is called

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DevNull SMTP, a Java-based "dummy" SMTP server. (The "DevNull" in the name means that e-mails are not actually delivered anywhere; they are simply disposed of.)

If you have connectivity problems between desktops and your SMTP server, you can use DevNull SMTP to examine the conversation between the client and server. For example, you can determine if there's a problem because of a pre-existing network condition -- such as packet sizes or other oddball network problems that aren't apparent at first.

DevNull SMTP works from a browser, or from the command line using a downloaded .JAR file. Once the program is running, click the "Start Server" button to allow it to accept incoming connections. If you want, you can edit the incoming port number and IP addresses that are allowed to connect to the server.

Conversations between the server and clients are logged in the "SMTP log" tab:

8/30/05 1:22 PM - [       1] ************** New Connection from: 127.0.0.1 **************
8/30/05 1:22 PM - [       1] S <-- 220 DevNullSMTP server. We treat your e-mail with care; 8/30/05 1:22 PM
8/30/05 1:22 PM - [       1] C --> HELO Skuld2
8/30/05 1:22 PM - [       1] S <-- 250 localhost. Please to meet you
8/30/05 1:22 PM - [       1] C --> MAIL FROM: <xx@optonline.net>
8/30/05 1:22 PM - [       1] S <-- 250 OK
8/30/05 1:22 PM - [       1] C --> RCPT TO: <xx@optonline.net>
8/30/05 1:22 PM - [       1] S <-- 250 OK
8/30/05 1:22 PM - [       1] C --> DATA
8/30/05 1:22 PM - [       1] S <-- 354 Start mail input; end with <CRLF>.<CRLF>
8/30/05 1:22 PM - [       1] S <-- 250 Message queued for destruction.
8/30/05 1:22 PM - [       1] C --> QUIT
8/30/05 1:22 PM - [       1] S <-- 221 Good bye. Hope to see you again
8/30/05 1:22 PM - [       1] ~~~~~~~~~~~~~~ Connection closed: 127.0.0.1 (16 ms)~~~~~~~~~~~~~~

About the author: Serdar Yegulalp is editor of the Windows Power Users Newsletter.

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This was first published in October 2005

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