7 email blocked list prevention practices for businesses

Email blocked listing is a major problem, but sometimes overlooked in the conversation around spam and email threat prevention. The impact on a business can be devastating if it isn’t caught in time, especially if the company relies on email marketing for lead generation and customer correspondence. While it’s possible to recover from the effects, it’s a complicated process and may set back productivity in the meantime. That’s why it’s important that managed services providers (MSPs) take proactive steps to prevent this from happening to their clients in the first place.

What Is an email blocked list?

A blocked list is a list of email addresses that are blocked from communicating with or logging into a network, computer, domain, or site because they have been identified as known sources of spam. In addition to email addresses, these lists can include IP addresses of servers known to send spam, as well as domains, user IDs, MAC addresses, or programs.

Blocked lists are a common feature of spam filters, antivirus software, and intrusion detection systems. They are designed to help prevent possible attacks and are, in theory, a useful and effective cybersecurity feature. However, businesses can end up on the receiving end of that feature, often through no fault of their own. For instance, hackers or botnets may have used their business email accounts to send spam to customers. Once blocked, the company’s sent mail will not be received regardless of the legitimacy of the content. That means your recipients won’t receive your messages, potentially bringing your business activity to a standstill and preventing you from exploring new contacts and opportunities.

Types of email blocked lists

Depending on the situation, a company may end up on one or more of these types of lists:

  • Public: There are about 120 publicly available lists, making them the easiest ones to check yourself. They can be IP-based or domain-based.
  • Enterprise Spam Firewalls: These are a subset of public lists that are part of the spam firewalls of business IT departments.
  • Private/ISP: Major ISPs, like Gmail, Yahoo, and Outlook, usually keep their own internal lists. While some will let you check if you’re on it, most will not.

You’re probably wondering—how do I find out if my email is blocked listed? The ease of checking whether you’re on one of these lists varies based on the type. The easiest way to check is by using an email check website. These sites will cross-reference the IP or domain name in question with the most popular lists to determine whether you’re in the clear. Some of the top checker sites are, MXToolBox, MultiRBL, or even Google-Postmaster for domain reputation. You can manually input your info on these sites for more insight.

You may also be able to check if you’re blocked by monitoring inboxes and email server logs. In many cases, you’ll see a high rate of email bounces and lower delivery rates. Check SMTP error counts on bounce back emails, as these might come from ISPs or specific blocked listing services. This is a manual solution, so it doesn’t necessarily help you scale up your protection efforts—it just gives you some initial insight into the problem.

6 best blocked list prevention practices

While it’s usually possible to determine if you’ve been blocked listed and remedy the situation, the best and easiest approach is to make sure you never get blocked in the first place. These practices can help:

1. Engage in spam filtering for outbound messages

When it comes to spam filtering, the focus is almost always on filtering inbound spam emails. While that’s certainly valuable when it comes to cybersecurity, if you’re serious about preventing blocked listing, filtering outbound spam is just as important. Outbound spam can lower your network reputation, potentially leading to emails not going out. The good news is that outbound spam filtering, which is a feature of N-able Mail Assure, helps stop viruses and spam from being sent out by accounts in your customers’ systems—accounts that have usually been hijacked by malware or bots. The tool’s abuse management feature shows you which accounts are sending out the spam so you can shut them down before they get the IP address blocked listed.

2. Clean your contacts list regularly and avoid typos

Effective list management is an essential step for avoiding spam traps and keeping your emails off blocked lists. Remove bounced email addresses right away, as continual bounces can get you flagged. Similarly, check for any subscribers who haven’t engaged with the company for six months or more, send them a reengagement email, and remove them if they are unresponsive. You should also regularly check for any typos in your addresses to make sure you don’t have any invalid contacts contaminating your list.

3. Personalize content

By reducing the number of generic messages you send out, you reduce the chances a recipient will mark your emails as spam. You should start by including a clear and informative subject line and be sure to incorporate valuable content and clean HTML structure in the email itself.

4. Attach an unsubscribe link

Make sure you’re always following anti-spam laws. That includes having a clearly visible unsubscribe link. That link doesn’t just ensure you’re following the law, it can also improve the user experience, which means a lesser chance of being marked as spam.

5. Secure the server

Failing to secure your server can get you blocked listed even if you follow all the best email marketing practices. If it’s insecure, malware or bots can easily hijack your email and start sending spam from it, earning you a spot on a blocked list fast. Outbound spam filtering delivers threat protection that helps you quickly catch a malicious attack.

6. Avoid spam traps with opt-in lists

Use opt-in email lists to avoid the possibility that you’re sending messages to spam trap addresses. These traps appear ordinary, but they are specifically set up to catch businesses who are sending unwanted emails. If you hit one of these accounts, you’ll likely end up in trouble and it can be difficult to recover.

7. Archive your emails for continuity

This will help you reduce the impact of blocked listing if it does occur. Email archiving, which encrypts and stores your data securely, plus mail continuity services, ensure that no matter when your issues are cleared up, all of your emails will be delivered to their intended recipients. Plus, email archiving can help you work towards regulatory compliance, including SOX compliance.

Preventing customer email blocked listing

Clearly, prevention can be tricky. And for MSPs who handle a number of customers, trying to manually manage IP address reputation can quickly become overwhelming. That’s why you need a hosted IP blocked list prevention solution that will keep bad emails from coming in and from going out.

N-able Mail Assure is built to help you better manage outbound spam with abuse management features that help identify, control, and shut down accounts attempting to send it. Plus, the tool’s archiving and continuity services help minimize the impact for any blocking that does occur.


© 2021 N-able Solutions ULC and N-able Technologies Ltd. All rights reserved.

This document is provided for informational purposes only and should not be relied upon as legal advice. N-able makes no warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information contained herein.

The N-ABLE, N-CENTRAL, and other N-able trademarks and logos are the exclusive property of N-able Solutions ULC and N-able Technologies Ltd. and may be common law marks, are registered, or are pending registration with the U.S. Patent and Trademark Office and with other countries.  All other trademarks mentioned herein are used for identification purposes only and are trademarks (and may be registered trademarks) of their respective companies.

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