Email Blocklists: What They Are and How to Avoid Them

We’ve said it once, and we’ll probably say it 100 times more: email deliverability is the elephant in the room for email marketing. 

Blocklists play a significant role in deliverability. And as far as blocklists are concerned, email content isn’t the only factor determining if a domain is blocklisted.

In this post, we’ll go over what a blocklist is, how domains end up on blocklists, how to delist a domain name, and some best practices to avoid landing on the blocklist.

A blocklist is a collection of IP addresses, email addresses, or domains that have been flagged as sources of spam messages or harmful content. Email clients, email service providers (ESPs), and email servers usually block messages from domains or addresses on IP blocklists. Internet service providers (ISPs) sometimes prevent users from accessing blocklisted websites. 

Some popular blocklists include:

• Spamhaus
• MXToolBox
• Barracuda Reputation Block List (BRBL)
• Spamcop
• URIBL
• Google Transparency Report
• PhishTank

Email blocklists may also be referred to as blacklists. However, most of the email industry has moved away from using this term to avoid unintentional negative connotations.

The goal of a blocklist is to protect users against spammy, malicious, or harmful content. Here are some common reasons why a domain might land on the blocklist:

• The domain is sending out spammy content.
• The domain’s subscribers have submitted spam complaints by marking the domain’s emails as spam.
• The domain is suddenly sending out a massive amount of emails.
• Emails sent from the domain have a high bounce rate.
• Users aren’t engaging with emails sent from the domain.

Keep in mind that blocklists can flag domains and email addresses with good intentions. Plenty of domains land on blocklists, even if they’re steps to avoid them. Luckily, blocklisting is usually temporary.

Running a domain blocklist check on your email or domain helps find whether your domain (or other domains in your message) is on a blocklist. You can run your domains manually through individual blocklists or save some time by using a tool that checks your email against multiple blocklists at once.

In Email on Acid’s Campaign Precheck, you can use a domain blocklist check against four major blocklist services: Spamhaus, Phishtank, Google Transparency Report, and URIBL. We’ll let you know if your domains are on any blocklists. 

Email on Acid’s tool helps you catch blocklisting issues before you send a campaign. But Mailgun Optimize takes things a bit further with Deliverability Monitoring. You don’t want to find out you’ve been blocklisted right before you launch a big campaign, so our Mailgun Optimize suite is the perfect solution as it lets you keep tabs on multiple IPs at all times.

If you find yourself with a blocklisted domain, most blocklists offer advice for delisting your domain. Spamhaus, for example, offers a “Blocklist Removal Center” where you can enter your IP address or domain name and find information on how to get off the blocklist.

Mailgun Optimize Deliverability Monitoring also offers actionable advice if you’re blocklisted, so you’re delisted as soon as possible.

After delisting, you may want to look at your email content and follow our best practices for sending emails. Check out our list of do’s and don’ts below.

Do:

• Keep a healthy subscriber list. Clean up your contacts. Try re-engagement campaigns to activate dormant subscribers and remove those who don’t respond. 
• Segment and personalize your email content for specific interests, customer types, and purchase history. This will help keep your subscribers engaged. Relevant emails mean fewer spam complaints.
• Have an easy-to-find unsubscribe link in every email.
• Consider an email preference center, so your subscribers can choose what type of emails to get from you and their frequency.
• Use double opt-ins to avoid spam traps like honeypots.
• Use email authentication protocols to prove your identity as a sender with mailbox providers.

Don’t:

• Do anything that makes you look like a spammer (i.e., overuse of ALL CAPS, exclamation points, and spammy language)
• Use poorly formatted HTML. Clean up your code.
• Rely on all-image emails. Try to maintain a balance between images and text
• Purchase an email list. (Don’t do this. Ever.)

Aside from content, you can use email authentication protocols to avoid landing on a blocklist. That includes DomainKeys Identified Mail (DKIM), Sender Policy Framework (SPF), and  Domain-based Message Authentication, Reporting and Conformance (DMARC). These help the mailbox provider confirm that the message is legitimate and coming from a trusted sender. 

Besides following the best practices above, we have one last piece of advice for avoiding landing on a blocklist: run spam tests and monitor deliverability!

Always run spam tests and blocklist checks, even if you’ve sent the email before. Spam filters and blocklists are always changing and updating, so an email that made it to the inbox yesterday could be spam tomorrow.

With Email on Acid’s Spam Testing, you can check your emai against the most common spam filters and blocklists to ensure your message reaches the inbox. Then, get super serious about deliverability with Mailgun Optimize, including ongoing blocklist monitoring for multiple IP addresses. 

We’ve said it once, and we’ll probably say it 100 times more: email deliverability is the elephant in the room for email marketing. 

Blocklists play a significant role in deliverability. And as far as blocklists are concerned, email content isn’t the only factor determining if a domain is blocklisted.

In this post, we’ll go over what a blocklist is, how domains end up on blocklists, how to delist a domain name, and some best practices to avoid landing on the blocklist.