Email blocklists are everywhere. They rank from the formidable to the obscure. The exact number of blocklists is not fully known – there are at least hundreds. Reputable blocklists carry weight amongst the email receivers of the world and can negatively impact delivery, while other, more obscure blocklists hold little sway and do not have much of an impact on a sender’s ability to get in the inbox.

With so many blocklists out there, being listed is usually a question of when and not if for most marketers. To put it bluntly, Blocklists Happen. So which ones should you most be concerned about and, more importantly, how can you stay off them? Let’s take a look.

Blocklist Basics

An email blocklist is defined as any group of IPs or sending addresses that are suspected of email spam activity. Blocklists exist to protect users from spam messages and allow legitimate email to be delivered (and get the attention it deserves).

There are two types of blocklists: IP blocklists and domain blocklists. IP blocklists are concerned with the source of the message (the sending IP), while domain blocklists are concerned with the source of the links inside the message. Typically, honest senders see more trouble with IP-based blocklists than they do with domain-based blocklists.

The Usual Suspects: IP Blocklists

There are several main blocklists you should be concerned about staying off of, as a sender, including the ones listed in this section.

Spamhaus: The Alcatraz of Blocklists

Want to keep a spammer up at night? Just mention the name “Spamhaus.” Using advanced tactics, Spamhaus protects hundreds of millions of inboxes from unwanted messages. Unlike many blocklists, which have easily accessible avenues for remediation, being listed on Spamhaus ensures a lengthy, complicated process for removal. Just like “The Rock” that once housed Al Capone, the best way to get out of a Spamhaus listing is to never get on it in the first place.

Senders can wind up on Spamhaus by sending to Spamhaus spam traps, or being reported by a receiver as a spammer. To avoid this, make sure you maintain clean data and practice opt-in only marketing campaigns. Spamhaus is used by many major ISPs, including Gmail; if you get listed, it won’t be easy, fast, or inexpensive to mitigate the drastic effects on your deliverability. You’ll need to come up with a plan, share it with Spamhaus, and prove to them that you’re following it.

SpamCop: Trapping Spammers Since 1998

One of the most active spam trap blocklists is SpamCop. While it’s possible to be listed on this blocklist by getting too many spam complaints registered against you, the most common way to wind up on SpamCop is by sending to one of its spam traps.

SpamCop maintains a wide network of spam traps (email addresses created solely to catch spammers). The best way to stay off SpamCop is to never purchase or rent data, and to perform regular list cleaning. SpamCop’s listings generally last for 24 hours, with automatic delisting available as long as you don’t send to another spam trap within 24 hours of the initial listing. During a listing you can expect to see increased bounces at the domains that participate in the SpamCop network, limiting the ROI of your marketing campaigns.

If you do find yourself listed on SpamCop, the best step you can take is to stop sending right away and immediately clean all your lists. While it’s not always perfect, list cleaning will remove known spam traps from your database.

Other Email Blocklists

As mentioned, there are hundreds of known blocklists in existence today. Other common IP blocklists include Invaluement (ivmSIP) and Truncate. The severity of a blocklist and its avenues for delisting vary by the source, but the best way to stay off blocklists is to maintain clean data, send only to engaged subscribers, and maintain low spam complaint thresholds.

Want to learn more? Read the complete article on our partner Act-On Software’s blog.

Need help with your email deliverability? Contact us today to learn more about how Goose Digital can help.