How to Create Your Own Email SMTP


Often it is necessary or desirable to operate your own SMTP (Simple Mail Transfer Protocol) server for sending email. This can be needed when your ISP or employer doesn't provide this service. Some email programs and system monitoring or other software programs require SMTP for sending messages and alerts, and you might have to build your own SMTP server to accommodate them.

Things You'll Need

  • Computer
  • Mercury Mail Transport software (free download)
  • Access to your router

Setting Up Your Own SMTP Server

  • SMTP operates using TCP port 25. You will need to make sure this port is open through your Internet connection. Consult your router's programming instructions to learn how to forward this port to the machine that will be running the mail server software.

    You also need to be sure your ISP allows traffic on port 25. If you are not sure, you can use a free tool from to check if this port is open. Run this tool after making the necessary changes in your own router.

  • Download and install the Mercury Mail Server. Several questions will be asked as you install the program. You need to have complete knowledge of your network and ISP connection to answer these questions correctly.

    The most important question you will be asked is whether to install the SMTP "relay" client or "end-to-end" client. The answer lies in the services provided by your ISP. If your ISP does have an SMTP server available for your use, you can install the "relay" client. (In most cases, if you have an SMTP server available from your ISP, you won't need to install your own mail server.)

    If they do not provide this service at all, or it doesn't meet your needs, you will need to install the "end-to-end" client. This client does not need to use your ISP's mail server. Instead, it looks up the address of the recipient's mail server and delivers each message directly to that server.

  • Configuration of Mercury when using the relay client is fairly simple. There are a lot of parameters you can change, but you probably won't need to change many of them for a basic installation.

    The most important parameter in the relay client setup is your "smarthost" settings. This is the SMTP server provided by your ISP. You will need the server address, port number (usually port 25) and possibly a username and password.

    The end-to-end client is easier to configure. But in both cases, there are a few additional parameters you will need to set up. Consult Mercury's "Help" menu and the online support community if you get stuck.

  • After configuring Mercury, you are ready to test it. From the "File" menu, select "Generate Test Messages." Enter your email address for the recipient address, enter "test" for the subject and press "OK." The system will send you a test message with that subject line, and the body of the message will contain a lot of text taken from various sources, including public domain books. If you receive this message, you have configured the client properly.

  • Next, go to your email program (Outlook, Outlook Express, Pegasus Mail, etc.) and set up Mercury as your "Outgoing Mail" server. Simply put the machine name or IP address as the hostname and you're done. Test it and watch Mercury's dialog boxes to see how your message flows through the system and out to the Internet.

    Of course, if you choose to perform a more complex Mercury installation (Mercury can be a full-function mail server, including receiving mail and distributing it to multiple users), you may have more configuration to do before you can use the program to send mail. But if you have done a basic setup as described here, you should be ready to go.

Tips & Warnings

  • Mercury is a full-featured email server and can be confusing to set up if you don't review the documentation first. There are several things pointed out in the manual that will save you much grief if you know about them ahead of time. Read the manual.
  • Google's Gmail service has a free and open SMTP server you can use. This service requires special configuration; see the Reference section for details.
  • Do a Google search for "free smtp mail server" and you will find there are several other options available. Try more than one and see which one is best for your needs.
  • If you plan to use your SMTP server to send spam email, be warned: Your ISP will likely be monitoring traffic for spam, and some recipients of your spam will report your IP address. Spam is illegal in the United States.
  • Mercury is free for non-commercial use; a small licensing fee is requested for commercial use.

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