Email blacklists (also known as blocklists or block lists) are everywhere. They rank from the formidable to the obscure. The exact number of blacklists is not fully known – there are at least hundreds. Reputable blacklists carry weight amongst the email receivers of the world and can negatively impact delivery, while other, more obscure blacklists hold little sway and do not have much of an impact on a sender’s ability to get in the inbox.
With so many blacklists out there, being listed is usually a question of when and not if for most marketers. To put it bluntly, Blacklists Happen. So which blacklists should you most be concerned about and, more importantly, how can you stay off them? Let’s take a look.
An email blacklist is defined as any group of IPs or sending addresses that are suspected of email spam activity. Blacklists exist to protect users from spam messages and allow legitimate email to be delivered (and get the attention it deserves).
The first blacklist was created in 1997 by Internet Hall of Fame inductee (yes, that is a real thing), Paul Vixie. The “Real-time Blackhole List,” as he called it, was formed as a response to the overwhelming growth of spam that occurred during the Internet boom. With no government action on spam email taken until 2003’s CAN-SPAM Act, it was up to Vixie and other Internet titans to take up the battle. Since 1997, hundreds of other blacklists have popped up to help in the ongoing effort to curtail spam messaging.
There are two types of blacklists: IP blacklists and domain blacklists. IP blacklists are concerned with the source of the message (the sending IP), while domain blacklists are concerned with the source of the links inside the message. Typically, honest senders see more trouble with IP-based blacklists than they do with domain-based blacklists.
The Usual Suspects: IP Blacklists
There are several main blacklists you should be concerned about staying off of, as a sender, including the ones listed in this section.
Spamhaus: The Alcatraz of blacklists
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 blacklists, 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 blacklists is SpamCop. While it’s possible to be listed on this blacklist 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 blacklists
As mentioned, there are hundreds of known blacklists in existence today. Other common IP blacklists include Invaluement (ivmSIP) and Truncate. The severity of a blacklist and its avenues for delisting vary by the source, but the best way to stay off blacklists is to maintain clean data, send only to engaged subscribers, and maintain low spam complaint thresholds.