Fighting spam with fake MX records

No junk mailSpam is a well known problem to all users of the Internet, especially technical administrators of Internet services. I own several domain names for different purposes. Some are used for websites, some are used for e-mail, some are used for both, some are used for infrastructure (e.g. mapping easy to remember hostnames to IP addresses), and some are just sitting for future use. Most of my domains are not used for receiving e-mail. However, spammers don’t care and will still send spam mails to these domains. Even without Mail eXchange (MX) records a domain is still not safe as many e-mail servers will instead tryout the A record of the domain. With several domains not used for e-mail, this can at times be annoying to manage and causes extra server load.

To minimize the problem, using fake MX records, known as ‘nolisting‘ has been proposed as a trick to reduce spam.

I’m currently using a free service offered by Junk Email Filter Inc. They are running the project Tarbaby, essentially a cluster of fake MX servers. The project has two goals: 1) to help reduce incoming spam, and 2) to support the ongoing work of maintaining the Junk Email Filter blacklist of known spam sources.

The service is very simple to setup and use. Simply add the following hostname as the only MX record of the given domain:

tarbaby.junkemailfilter.com

You can set any value as the priority, for example, 10.

Every time a mail is received the system will respond with the code 550, which means that the message was not deliverable. Genuine senders will receive a reply with an error message and know that a given address is not available, and spam bots will move on and get registered in the blacklist.

Another free service is Fake MX. Add the following hostname as the MX record of the given domain:

mx.fakemx.net

Set any value as the priority, for example, 10. If you use more than one MX record, set the Fake MX record with a higher priority than the primary MX record. Also remember to read their terms of use before adding their mail server.

Using fake MX records is no ultimate solution to avoid all spam from getting in touch with your severs, but anecdotical experiences reported from different forums indicate that fake MX records significantly reduces spam.

More information about using fake MX records can be found at “Nolisting: Poor Man’s Greylisting” and “Other Trick For Blocking Spam.

As it is the case with most tricks also the nolisting strategy has some drawbacks. Especially if using a fake MX setup on a domain intended for receiving e-mail. Some of the drawbacks can be found at the Wikipedia page ‘Nolisting‘.