Occasionally I’ve had to troubleshoot sending email messages to a particular SMTP server by simulating a mail client (or .NET mail code) by using the telnet client. Here’s how I do it on Windows:
- Open the command prompt
- type: telnet smtpserver.domain.com 25 <press enter>
- type: helo domain.com <press enter>
- type: mail from: [email protected] <press enter>
- type: rcpt to: [email protected] <press enter>
- type: data <press enter>
- Write a test message. Typically, I type something like: hello world! <press enter>
- To send the message, type a single period (.) on a like by itself and <press enter>

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