Earlier this spring, we shared 5 resources that can help you keep track of your sending reputation. Another good way to keep a check on your reputation is to find out if you are on any blacklists (a.k.a. blocklists).

Blacklists contain lists of IPs or domains that pose a threat to consumer inboxes. Your email service provider may automatically alert you if you’re added to one, but it’s good to check for yourself. If you are on a blacklist, act quickly. Just a few spam complaints can add a legitimate sender to a blacklist.

Here’s an example of what it looks like to get blocked (red line):

Blacklist Resources

There are a lot of blacklists, but a good starting point is checking to see if your IPs or domains are on any of these popular lists:

  1. Barracuda Reputation Block List: BRBL is a free DNS blacklist (DNSBL) of IP addresses known to send spam.
  2. Invaluement: The Invaluement anti-spam DNSBL blocks elusive types of spam where the sender is sending unsolicited bulk email and escaping traditional detection methods.
  3. MXToolBox: MXToolbox shows you whether or not your domain or IP address is blacklisted and can perform checks on your DNS to see how it is configured.
  4. MultiRBL: This free multiple DNS blacklist service cross-references other blacklists by IPV4, IPV6, or by domain.
  5. Spamcop: The SpamCop Blocking List (SCBL) lists IP addresses that had mail reported as spam by SpamCop users.
  6. Spamhaus: The Spamhaus Project maintains a number of DNSBLs as part of their effort to identify and track spam sources, and provide anti-spam protection. To be removed from this list, visit their blocklist removal center.
  7. SURBL: Unlike most lists, SURBLs are not lists of message senders. SURBLs are lists of websites that have appeared in unsolicited messages.

How Blacklists Know You’re Sending Unwanted Mail

I recently asked one of email deliverability consultants, Luke Martinez, for some more context on how senders get added to blacklists and what you can do to protect your reputation. Here’s what he had to say:

“All blacklists have different ways of determining whether or not a sender should be listed. But almost all of them use some combination of spam traps and recipient feedback. Many blacklist operators manage large networks of spam traps (email addresses that are valid, but have never signed up to receive mail, or addresses that have been inactive for an extended period of time and should no longer be receiving email). The blacklist operators will monitor these addresses and blacklist any IPs or domains that send excessive amounts of mail to them.

Blacklist operators also work off of user feedback. A blacklist operator can trigger a listing if they receive an excessive amount of direct abuse complaints about mail coming from your IP or your domain. The key to avoiding blacklists is to make sure you are sending mail people want, removing non-engaged users from your mailing lists, not purchasing, renting, or sharing address lists, and using a confirmed opt-in strategy for collecting addresses.”

Staying on top of your reputation by regularly monitoring your presence on blacklists and analyzing your engagement metrics can help clear your path to the inbox. SendGrid knows how important your reputation is, so our technical account managers and delivery team help to monitor blacklists on behalf of our customers and our 24/7 global support team is always ready and willing to help with questions.

For more information on how to monitor your reputation and comply with the ISPs, read our guide: The ABCs of ISPs and for more advice from Luke, check out his recent webcast: Great Expectations: Setting Your Email Marketing Up for Success.



Jillian Wohlfarth
As SendGrid's Director of Content, Jillian is responsible for ensuring that SendGrid provides valuable thought leadership content through the blog, whitepapers, webcasts, and more. When not writing and editing, you can find Jillian frequenting Denver restaurants in search of the best queso.