Blacklists 101: What They Are and How They Work

Clea Moore
Oct. 31, 2016 by Clea Moore

Blacklists 101 - stairs leading to do not enter sign

Blacklists

It’s that time of year again. Marketers are planning for the holidays; looking at how they can drive more revenue through email. It’s very common to see people mailing a little deeper into their files than they normally do, in an effort to reengage the people who haven’t purchased or interacted in a while. It’s easy to overstep the bounds of email best practices, and get yourself into trouble. That trouble commonly comes in the form of a blacklisting.

What is a blacklist?

A blacklist is essentially a list of bad actors. Those bad actors are generally spammers, but any legitimate mailer who doesn’t adhere to best practices can be impacted. Blacklists can be domain-based, URL-based, or more commonly, IP-based. They are generally run by independent operators, or organizations whose customers are ISPs, hosting companies, or corporate mail managers.

How do you get listed?

Blacklist operators most commonly use networks of spam traps to catch spammers and marketers behaving badly. (Check out the series I wrote about spam traps earlier this year for more info.) Mailing to spam trap addresses is a signal that you have poor list hygiene practices, since those addresses don’t belong to real users. Depending on the type of trap you mail to (or hit) and the number, you may get flagged as a bad actor and end up on a blacklist. In some cases this is an automated process, in others (generally in more severe cases) it’s manual.

What happens when you get “listed” on a blacklist?

A blacklist is commonly used by mail receivers (ISPs, hosting companies, etc.) to block unwanted mail from bad actors. The amount of mail blocked depends on which blacklist listed you. Some are more impactful than others, based on which mail receivers use them. Spamhaus, for example, is the most widely known blacklist and is used by some of the major mailbox providers. So a Spamhaus listing will have a big impact on your program.

What can you do to resolve a blacklisting?

Each blacklist has it’s own removal process, which can be automated or manual. Either way, it’s important to understand what caused you to get listed in the first place. Did it happen right after you mailed to an old, inactive file? Are you working with a new affiliate? Is a suppression process broken? Once you have identified and resolved the issue that caused the listing, the next step is to reach out to the blacklist operator via their process to request removal.

What should you do to avoid blacklists in the first place?

The best way to avoid the blacklist is to mail to recently engaged users. We recommend those who have opened or clicked in the last 90 days. It’s understandable that marketers want to leverage their email programs to increase sales during the holidays, so a 90-day activity window isn’t always doable. If you do end up reaching deeper into your list, you shouldn’t be including anyone who hasn’t engaged in over a year. Past that time, you run the risk of hitting recycled spam traps (once engaged users, now long-dormant accounts). In addition to a short activity window, double opt-in (or COI) is a great way to avoid mailing repeatedly to spam trap addresses, since they won’t click the confirmation link. We also highly recommend that you use a reCAPtCHA at sign-up to mitigate malicious signups.

Things to keep in mind…

Having a way to monitor your IPs and domains for blacklistings is always a good idea. At Sparkpost, we proactively monitor listings for our Premium and Enterprise customers using the 250ok platform. Also, as I alluded to above, not all blacklists have the same impact on your program. If you see a listing through a monitoring service or in your logs, check your stats in the Sparkpost UI (blocked messages) to gauge the severity of the listing. While you might not see a big impact from some smaller blacklists, they can be a good signal to let you know something is off with your program that might turn into a bigger headache down the road if you don’t address it.

— Clea

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