How to Find Out If an E-mail Server Receives Inbound Connections

If you ever set up an e-mail server and tried to send e-mails to it from the Internet, you may have felt frustrated when nothing arrives into your inbox. Follow these instructions to learn just how straightforward it is to find out if you can establish a connection to it. Remember, there are a number of steps that must be accomplished before an e-mail server will send and receive e-mails. Though that is beyond the scope of this article, the steps here will help you establish if a connection to your e-mail server is possible.

Difficulty: Moderately Challenging

Instructions

Things You'll Need:

• A PC with Windows XP or other other Operating System (OS) where the command Telnet is available
• The IP address of your e-mail server, such as 69.147.102.58, or else a DNS name that will resolve into the server IP address, such as smtp.mail.yahoo.com or similar

1. Click "Start." A toolbar or a window will come up.

2. Click "Run." A window will come up with a place to type a command or other text.

3. Click on the rectangle (or text field, as it is called) and type this command: "cmd." Press "Enter," or click "OK." A black window will (usually) come up. In it it will have a blinking cursor. This window has the title "Command Prompt."

4. Click the title bar or anywhere else inside this window, to select it (or "give it focus"). You should be able now to type commands into it.

5. In the Command Prompt window, type this command, where (IP address) is replaced by your IP address or DNS name: "start telnet (IP address) 25." Let's study the meaning of each word, or parameter, as they are known. Start allows the command you type next to come up in a separate window.
   Telnet is a (text) terminal emulation program that uses TCP/IP instead of a serial cable to connect to computers. (IP address) is replaced by your 4-number set, also known as the dotted quad. It is the Internet equivalent of a phone number. It can also be replaced by your DNS name.
   25 is like the extension number (or TCP port number, as it is known) used for inbound e-mails.
   
   Examples: "start telnet 69.147.102.58 25" or, "start telnet smtp.mail.yahoo.com 25."

6. Once you type your Telnet command, press "Enter." A new black window will come up, with the title made up of the word Telnet and whatever you have typed as your IP address. Inside this new window you may see the words Connecting to (whatever you typed).

7. If whatever parameter you typed after the command Telnet is actually an e-mail server, you will get some text like this: "220 smtp101.plus.mail.re1.yahoo.com ESMTP."
   
   Contents will vary depending on what technology (and customization) your e-mail server had. But "by law" (actually, by protocol, one known as SMTP), it must start with the number 220 and a space.

8. OK; so now you know there is some sort of service at your IP address or DNS name, and your proof is right in front of you. What now?
   
   To close this window, you simply type this SMTP command: "quit." Whatever you connected to will answer something like, "221 smtp101.plus.mail.re1.yahoo.com."
   
   As before, our SMTP protocol dictates that responses MUST start with a number and a space.
   
   Afterwards--usually immediately--your e-mail server will close your connection. Your Telnet program may report it as "Connection to host lost" Shortly thereafter, it will close your Telnet window. You should be back to your previous "Command Prompt" window.

Tips & Warnings

• You can find out if your own PC (Personal Computer, usually running Windows) has an e-mail server. You can type this command in your command prompt: "start telnet localhost 25." You may surprise yourself by finding one. In my PC (actually, a laptop), I found nothing, even when Microsoft Outlook Express was open. The parameter LocalHost (by protocol, once again) must point to your own computer. However, few services actually work on(or bind to) it.
• You can also find your PC IP address with this command: "ipconfig." Then test that one.

Resources

• The SMTP protocol - the authoritative reference to sending and forwarding e-mails on the Internet

[MidniteWriter]

on 1/27/2008 Good info, thanks!