How to Send Email Using Telnet:

Software like Thunderbird and Outlook make sending e-mail seem like magic. Well, until your e-mail never arrives at its destination. How can you find out what really happens when you click “Send?” One option is to send a test message from your e-mail provider's outbound server with telnet, a tiny application that came with your computer. You may catch an error message that your e-mail software didn't.

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EditConnecting to the Mail Server with Telnet

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   Get telnet. If you’re using MacOS or Windows XP, your version of telnet is ready to use. If you have Windows Vista, 2008 server, 7, 8.1 or 10, you’ll need to enable telnet before you can use it.

   • Windows Vista, 2008 server, 7 and 8.1: Click on the Start Menu and then select Control Panel. Click Programs, and select “Turn Windows features on or off.” This will bring up a list of Windows Features. Scroll down until you see “Telnet Client,” and put a check in that box. Click “OK.” ^[1]
   • Windows 10: Right-click the Start menu and select Programs and Features. Click “Turn Windows features on or off” in the left menu. In the list that pops up, put a check in the box next to “Telnet client” and click “OK.”
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   Open a terminal window. This is a little different between Windows and Mac.

   • Any version of Windows: Press ⊞ Win+R , type cmd, then press ↵ Enter.
   • Mac: In Finder, select “Applications,” then “Utilities.” Double-click the “Terminal” icon. ^[2] You can also access Terminal by typing it into Launchpad and clicking it.
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   Open a telnet connection. Type telnet mail.server.com 25 where "mail.server.com" is the name of the Simple Mail Transfer Protocol (SMTP) server of your email provider (such as smtp-server.austin.rr.com) and 25 is the port number used by the SMTP service.

   • You should receive a reply like "220 mail.server.com.”
   • Port 25 is the port for most mail servers, but some network administrators move SMTP to a different port, like 465 (a secure port) or 587 (for Microsoft Outlook users) ^[3]. Ask your administrator (or check your account information) for the correct port.
   • If you receive an error message, such as "Cannot connect to host on port 25," and you are sure that port 25 is the correct port, the mail server is likely experiencing an issue.