How to Restrict Site Registration and Block Email Spam Domains

The internet is swarming with spammers dying to get their hands on your servers. Here’s how to stop them getting to your WordPress site.

Registering an account on your site is a relatively easy way for amateur spammers to break into your system and use it as part of their spamming strategy.

Whether human or bot machines, spammers would normally be using an email spam domain, therefore we cannot stress enough the importance of identifying those domains and blocking them in advance, which is relatively easy to do. If they catch you unprepared though, they can cause serious damage to your site.

How to Block Email Spam Through Your WordPress site?

There are several tools which can be used to restrict spammers such as CAPTCHA protection, email confirmation, security questions, and many other functions that add increased security measures to your site’s registration process. On top of this you can also restrict which domains are allowed to be registered in your site and which ones to blacklist.

This is a simple and highly effective prevention method that will block spamming attempts right from square one.

Identify and Block Email Spam Domains using SpamAssassin

SpamAssassin is part of the Apache Foundation. It uses a variety of spam-detection techniques, including DNS-based and fuzzy-checksum-based spam detection, Bayesian filtering, external programs, blacklists and online databases. SpamAssassin also publishes a list of free email domains which is available at this location.

Using this list as a way to prevent spammers can help reduce the number of registrations from free email domains, which are often used by spammers as they tend to be less supervised. Bear in mind though, that not all free email domains are necessarily spamming domains, and Gmail.com is only one of many cases.

Looking at spam assassin’s listings, you should take notice of the lesser known platform which have lower support and supervision and therefore likely to be used by spammers.

SpamHaus HomePage

Using Spamhaus DB Blacklist

The Spamhaus DBL is a realtime domain found in spam messages. The DBL is query-able in realtime by mail systems throughout the Internet, allowing mail server administrators to identify, tag or block incoming email containing domains which Spamhaus deems to be involved in the sending, hosting or origination of Unsolicited Bulk Email (aka “Spam”).

Using the DBL can help prevent spammers from registering into your site. However, making use of Spamhaus’s free public DNSBL service is restricted to low-volume non-commercial users only.

SpamHaus HomePage

Email Registration Blacklist Plugin

This plugin is based on both the services above (SpamAssassin and Spamhaus DB Blacklist), allowing WordPress website administrators to block registration attempts from one of the blacklisted domains appearing in these lists. The plugin also enables users to create their blacklists and manually add them whenever necessary.

Email Registration Blacklist Settings

Whitelisting Banned Domains

To override some domains which exist in the above lists, such as gmail.com, the plugin also comes with a manual whitelisting feature, allowing you to add specific domains so they can still be used for registering to your site.

Email Registration Blacklist User Whitelist