Using example domains

People have put example domains in all kinds of programs and servers, often using,, or – along with such as,,,,, and so on.

All of these are domains that resolve and have actual servers up and running on the Internet. Of those mentioned previously, only, and are preserved for testing purposes by IANA in RFC 2606.

Better yet, when using example email addresses avoid any surprises by using one of these domains specified in RFC 2606:

  • .example (for documentation)
  • .test (for testing purposes)
  • .localhost (for sending to the local host)
  • .invalid (for creating guaranteed invalid domain names)

If you use these domains, you won’t have to worry about mail going out that wasn’t supposed to go out. I’ve seen this happen before – a configuration file sent out with an open source server sends mail to an example address – which address turns out to go to a valid domain on the Internet, where it is accepted by the mail host.

Don’t get caught by this mistake! Use the RFC 2606 domains wherever needed, and don’t make one up of your own.

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