What Are Email Blacklists and How to Avoid Them

Most email marketers have found themselves on at least one IP or domain blacklist at some point. If you find yourself on a blacklist, it’s a good idea to assess your address collection practices, evaluate your sunsetting policy, and then request a delisting at the relevant blacklist removal form (if they’re available).

The impact of having your IP or domain on a blacklist can range from being a small annoyance to a complete showstopper for your email deliverability. Because deliverability is the primary concern for most email marketers, it’s important to have an understanding of how blacklists function, and what you can do as a sender to reduce your risk of being blacklisted.

How do email blacklists work?

To help you understand how a blacklist works, look at this Spamhaus diagram below.

For the most part, spam traps fall into one of three categories:

1. Recycled Spam Traps: These are email addresses that were once valid, but have been dormant long enough that they could not have engaged with any email in a long time. Messages sent to these addresses are typically refused (bounced) by the receiving server for a year or more before they are reactivated as spam trap addresses.

2. Typo Traps: These are email addresses that usually end up on recipient lists due to user error. Typing example@hitmail.com instead of example@hotmail.com. Similar to recycled spam traps, these addresses never open or click any of the messages they receive. The anti-abuse community believes sending excessive amounts of mail to typo traps is indicative of poor list acquisition practices, and poor list hygiene.

3. Pristine Traps: These are email addresses and domains that have never been used to actively sign up to receive email. Pristine traps most commonly end up on mailing lists when senders purchase, rent, or scrape addresses.

Note: Some email blacklists also list domains and IP addresses based on user-generated feedback and manual reporting of unsolicited emails.

How to find out if you’re on an email blacklist

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:

Barracuda Reputation Block List: BRBL is a free DNS blacklist (DNSBL) of IP addresses known to send spam.
Invaluement: The Invaluement anti-spam DNSBL blocks elusive types of spam where the sender is sending unsolicited bulk email and escaping traditional detection methods.
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.
MultiRBL: This free multiple DNS blacklist service cross-references other blacklists by IPV4, IPV6, or by domain.
Spamcop: The SpamCop Blocking List (SCBL) lists IP addresses that had mail reported as spam by SpamCop users.
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. 
SURBL: Unlike most lists, SURBLs are not lists of message senders. SURBLs are lists of websites that have appeared in unsolicited messages.

Reducing your risk of getting on an email 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.

You also need to be aware of how you’re adding new subscribers to your email list to ensure you’re not falling victim to spam traps.There are several things you can do to avoid them:

1. Confirmed opt-in: Before adding a new recipient address to your active mailing list(s), send a confirmation email.

Pros:

• Only valid, engaged recipient addresses will be added to your mailing list.
• Prevents typo traps, recycled spam traps, and pristine trap addresses from being added to your list.
• Increases open and click rates (because you’re sending email to recipients who explicitly asked to receive it!).
• Reduces spam reports and unsubscribes.
• Improves your ROI per message sent.
  

Cons:

• Possible reduction in marketing email opt-ins.
• Extra “friction” in the sign-up process.

2. Engagement-Based Sunsetting: Remove email address from your mailing list if they do not open or click a message in some period of time. This time period varies depending on factors like your industry and sending frequency.
   
   Pros:
   

• Removes “dead weight” from your email list.
• Improves sending reputation by only sending to recently engaged recipients.
• Improves ROI per message sent.
• Reduces spam reports and unsubscribes.
• Significantly reduces exposure to recycled spam traps and typo traps.
• Improves brand reputation by reducing the number of emails sent to people who don’t want them.

Cons:

• Significant technical requirements of determining who is engaged.
• Decreased list size.
• Potentially leaving money on the table. (What percentage of long-term non-engaged email recipients eventually convert to $$$?)

3. Real-Time Address Validation: Check email addresses at the point of signup for validity and common typos.
   
   Pros:
   

• Reduction in common domain typos.
• Reduction in pristine spam trap hits.
• Reduces instances of fake email addresses.
• Much less “friction” than confirmed opt-in.
• New signups tend to react positively to this kind of feature. (“Wow they caught my typo!”)
  

Cons:

• Licensing costs if using third-party service.
• Engineering and technical requirements if building your own verification logic.
  

Takeaways

The best solution for reducing your risk of ending up on a blacklist is different for every business model. Blacklists do not exist to make life more difficult for email senders. They’re here to help mitigate spam and keep recipients happy.

Remember that the purpose of email blacklists is to prevent email from being sent to inboxes that did not recently opt-in to receive email with explicit and informed consent. This means that no single preventative measure will guarantee zero blacklistings. But it also means that if you are doing everything in your power to send email that people truly desire, it will make the process of getting delisted that much easier!