What is an Email Blacklist?


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what_is_an_email_blacklistAn email blacklist, also known as a DNS-based Blackhole List is a real-time database that uses set criteria to determine if an IP is sending email that could be considered spam. There are several blacklists including Spamhaus, Barracuda Reputation Block List, and SpamCop to name a few, but they all have their own criteria for accepting inbound mail and all can have a negative affect on your delivery rate.

How a Blacklist Works

To help you understand how a blacklist works, you can take a look at this Spamhous diagram below. If the incoming mail fails to satisfy Spamhaus’ criteria for legitimate mail, the IP is then included on its list. Some ISPs opt to use this data to inform their filtering decisions and delivery of the email messages sent over that IP. It’s important to note that Spamhaus has no control over delivery or placement of your messages. The blacklist simply serves as a tool to help ISPs make their own decisions.

 

Spamhaus_Blacklist

How to Find Out if You’re On a Blacklist

If your email service doesn’t provide alerts when your IP has been added to a blacklist, then you’ll have to do it manually. Start by visiting the top DNSBL lists. These include:

  1. Spamhaus –The Spamhaus project is one of the most reputable blacklisting companies providing real-time anti-spam protection for internet networks worldwide.
  2. SURBL –SURBL is a second tier filter that works in conjunction with Spamhaus to identify some of the most difficult unsolicited messages to track.
  3. Barracuda Reputation Block List –BRBL is a free DNSBL of IP addresses known to send spam.
  4. Invalument –The Invalument anti-spam DNSBL is a subscription-based service that specializes in blocking elusive types of spam where the sender is sending 100% unsolicited bulk email and escaping traditional detection methods.
  5. Spamcop –The SpamCop Blocking List (SCBL) lists IP addresses that had mail reported as spam by SpamCop users.
  6. MultiRBL –This free multiple DNS Blacklist service that cross references other blacklists by IPV4, IPV6, or domain.

How to Get Off a Blacklist

High spam complaint rates are one of the main reasons that your IP ends up on a blacklist. So, it’s imperative that once you discover that you’re on one, that you take steps to get your IP removed from the list. By visiting each of these DNSBL sites, you can enter your IP to check your list status, and then obtain instructions on how to be removed. The key here is to be proactive. ISPs like to see that you’re trying to remedy your delivery challenges in a timely fashion. When you are on a blacklist, it’s best to have a deliverability expert (like those at SendGrid!) on hand to help you navigate the ISP landscape. ISP relations can help you get your program up and running faster so that you don’t lose valuable time trying to figure out what went wrong.

How to Stay Off a Blacklist

Reputation monitoring is the key to maximum email deliverability. By closely monitoring your complaint rates, you can prevent delivery failures before they happen. Check your stats with each campaign deployment and look for delivery dips and low engagement rates. Test out new campaigns, segment your users, and customize your content. These best practices will help ensure that you only send wanted email and stay off of blacklists all together.

To find out more about email delivery best practices, download our free Email Deliverability Guide.


Carly Brantz is a veteran in the email deliverability space working to make email simple and easy for developers by regularly writing whitepapers, research briefs and blog posts about email, technology and industry trends.

Carly Brantz on Twitter

4 thoughts on “What is an Email Blacklist?

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