When it comes to email, deliverability is important. A common reason for emails not being delivered is blacklisting: in this post, we’ll explore how to find out if you’re on a blacklist (a.k.a. blocklist), what you can do about it, and how to prevent it from happening.

Standard email analytics will tell you the basics on how customers are engaging with your email, but you may want to dig a little deeper to find out who is and who isn’t receiving your email, and why. This is where blacklists become important.

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 in danger of being added to a blacklist, act quickly. Just a few spam complaints can add a legitimate sender to a blacklist.

Once blacklisted, it will be substantially harder for your email to reach target inboxes, which will leave your marketing team at a significant disadvantage.

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

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. Spam traps are email addresses that are valid but have never signed up to receive email, 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 user feedback. A blacklist operator can trigger an action to list your company if they receive an excessive amount of direct abuse complaints about mail coming from your IP or your domain.

Protect Your Reputation: How to Avoid Getting Blacklisted

There are some basic activities to avoid if you want to keep your organisation off a blacklist. You should never purchase an email list from a third party, and the same goes for renting and sharing lists. You’ll have little information about the emails on this list, and the recipients won’t know why you’re sending to them, greatly increasing the likelihood of spam complaints.

Companies can take more proactive steps to avoid being blacklisted too. The key to avoiding blacklists is to make sure you are sending quality emails that people want. Provide them with quality content, and avoid misleading subject lines that will lead them to feel cheated. Actively maintain a clean database by using a double opt-in strategy for new emails and by removing non-engaged users.

Staying on top of your reputation by regularly monitoring your presence on blacklists and analysing your engagement metrics can help clear your path to the inbox.


By Luke Martinez, Email Deliverability Consultant at SendGrid. 

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