7 Critical Suppression Lists for Keeping Your Email Strategy on Track

Email marketing can be one of the most powerful tools in your arsenal for driving engagement, conversions, and customer loyalty. In fact, email generates $36 for every $1 spent, making it one of the most cost-effective marketing channels out there.

But here‘s the thing – email only works its magic if you‘re sending the right messages to the right people at the right time. And one of the biggest mistakes I see marketers making is neglecting their suppression lists and continuing to email contacts who are a poor fit or who have explicitly opted out.

This is a surefire recipe for tanking your email performance and damaging your sender reputation. Not to mention, it provides a poor experience for your contacts and can even put you at risk of violating privacy laws like GDPR.

The good news is, with a little strategic planning and the right suppression lists in place, you can avoid these pitfalls and keep your email program healthy and thriving.

In this guide, I‘m going to walk you through the 7 most important suppression lists every marketer should be using, along with tips and best practices for implementing them effectively. Let‘s dive in!

What Are Suppression Lists?

First things first, let‘s define what we mean by suppression lists. In simple terms, a suppression list is a list of email addresses that you proactively exclude from your email communications.

When you send an email campaign, you can select one or more suppression lists to ensure that any contacts on those lists will not receive the message, even if they would normally meet the criteria for the send.

Suppression lists are different from your main segmentation lists in that they are used for exclusion rather than inclusion. They allow you to fine-tune your email targeting and avoid sending messages to contacts who aren‘t a good fit.

Why Suppression Lists Are Critical for Email Success

Now you might be thinking – why would I want to purposely not email certain contacts? Isn‘t the goal to reach as many people as possible?

Well, not exactly. When it comes to email marketing, quality is more important than quantity. Sending emails to people who aren‘t interested or engaged can actually do more harm than good, leading to consequences like:

• Lower open and click rates, which can hurt your overall email deliverability
• Higher unsubscribe rates and spam complaints
• Damaged sender reputation with ISPs and email clients
• Skewed and inaccurate reporting on email performance
• Potential violations of anti-spam laws and regulations

On the flip side, using suppression lists to proactively exclude poor-fit contacts allows you to:

• Maintain higher engagement rates and positive sending signals
• Provide a more targeted, relevant experience for your subscribers
• Protect your sender reputation and inbox placement
• Gain cleaner, more actionable performance data
• Stay compliant with email regulations and best practices

In short, suppression lists are a key tool for optimizing your email strategy, prioritizing quality over quantity, and driving better results from your campaigns.

The 7 Suppression Lists Every Marketer Needs

Now that we‘ve covered the why, let‘s look at the how. Here are the 7 key suppression lists I recommend every marketer set up and maintain:

1. The Unengaged Contacts List

Over time, a percentage of your email list will naturally disengage and stop opening or clicking your emails. This is totally normal, but continuing to send to these inactive contacts can seriously drag down your performance metrics.

I recommend creating a suppression list of contacts who haven‘t engaged with your emails in the past 90-180 days (adjust the exact timeframe based on your typical sales cycle and email frequency). You can always try a re-engagement campaign down the line, but for your regular sends, it‘s best to exclude these folks.

Pro Tip: Use email engagement as a proxy for overall lead quality and prioritization. Contacts who are actively opening and clicking your emails are more likely to be high-value prospects worth investing more time and resources in.

2. The Bounced Email List

An email bounce happens when a sent message is rejected by the receiving server and returned to the sender as undeliverable. There are two types of bounces:

Soft bounces are temporary delivery failures that can happen if the recipient‘s mailbox is full, the server is down, or the message is too large. These can often be resolved by resending the message at a later time.

Hard bounces, on the other hand, are permanent delivery failures that indicate an invalid, closed, or non-existent email address. Continuing to send to hard bounced addresses can seriously damage your sender reputation, so it‘s important to suppress them ASAP.

Set up a suppression list that automatically adds contacts with hard bounced email addresses, and make sure to exclude this list from all your sends going forward. Most email service providers like HubSpot can automate this process for you.

3. The Unsubscribed List

This one should go without saying, but it‘s critical to honor unsubscribe requests promptly and completely. Not only is it required by law under regulations like CAN-SPAM, but it‘s also just good business practice. Continuing to email contacts after they‘ve opted out is a surefire way to annoy them and damage your brand reputation.

Make sure you have a master suppression list of all your unsubscribed contacts, and double-check that it‘s excluded from every single send. Again, most ESPs will handle this for you automatically, but it‘s worth verifying.

4. The Spam Complaints List

Getting marked as spam is one of the worst things that can happen to your email sending reputation. It‘s a major red flag to ISPs that your content is unwanted or inappropriate, and can quickly land you in the spam folder or even get you blocked entirely.

Create a dedicated suppression list for any contacts who have flagged your emails as spam. This shows that you respect their preferences and helps avoid any further damage to your deliverability.

Some key stats to keep in mind:

• A spam complaint rate above 0.1% can seriously impact your deliverability
• 53% of the email classified as spam by ISPs is flagged as such solely based on poor sender reputation
• It can take months or even years to recover from damaged sender reputation due to high spam complaints

So don‘t ignore those spam reports – suppress those contacts immediately and take steps to improve your email content and targeting to prevent future complaints.

5. The Competitors List

Most marketers don‘t want their competitors getting an inside look at their email campaigns and messaging. Even if they‘ve legitimately subscribed to your list, their motivations and behavior will be very different from your actual prospects and customers.

That‘s why it‘s a smart idea to maintain a suppression list of any contacts with email domains matching your known competitors. This both prevents competitors from stealing your ideas and keeps them from skewing your engagement data.

You can build this list manually based on your own market research and sales intelligence, or even automate the process using a tool like Clearbit to identify contacts from competitor domains.

6. The Bad Data List

Let‘s face it – no matter how clean you try to keep your email database, some bad data is bound to slip in. This could be anything from misspelled or fake email addresses to contacts with missing or inaccurate fields like name, company, or job title.

To maintain good email hygiene and deliverability, it‘s important to regularly identify and suppress contacts with poor quality data. Create a suppression list based on criteria like:

• Invalid or incomplete email addresses
• Missing key fields like first name or company name
• Contacts with obviously fake info like "Mickey Mouse" or "Acme Corporation"
• Duplicate records or email addresses

By excluding these contacts from your sends, you can avoid triggering spam filters and maintain a higher overall quality of your email list. Just be sure to also take steps to improve your data collection processes and forms to minimize bad data intake going forward.

7. The Rejected Leads List

Not every lead that enters your database is going to be a good fit for your product or service. Maybe they don‘t meet your key qualifying criteria, or maybe your sales team has already determined that they‘re not a viable prospect.

Rather than continuing to email these rejected leads with messages that aren‘t relevant to them, create a suppression list to exclude them from your main email flows. You can base this list on criteria like:

• Leads that have been marked as "unqualified" or "bad fit" by sales
• Contacts who don‘t meet your ideal customer profile criteria (e.g. wrong industry, company size, job title)
• Leads who have already been pitched by sales and declined to move forward

By segmenting out these contacts, you can focus your email efforts on your most promising leads and avoid wasting time and resources on those who are unlikely to convert.

Tips for Implementing & Maintaining Suppression Lists

Hopefully you‘re starting to see the power and potential of using suppression lists to optimize your email strategy. But how do you actually go about implementing them effectively? Here are a few key tips:

Start with the basics: If you‘re new to suppression lists, start by setting up the most critical ones like your unsubscribes, hard bounces, and spam complaints. These will have the biggest impact on your deliverability and sender reputation.

Sync with your sales team: Collaborate with your sales colleagues to identify any leads that should be suppressed based on their interactions and feedback. They can be a valuable source of intel on lead quality and fit.

Set regular update cycles: Aim to review and update your suppression lists at least once per quarter, if not more often. This ensures you‘re always working with the most current and accurate information.

Automate where possible: Take advantage of any features in your email platform that allow you to automate suppression list management, such as automatically excluding bounces or unsubscribes. This saves you time and reduces the risk of human error.

Use suppression lists in tandem with segmentation: Suppression lists are most effective when used in combination with a robust segmentation strategy. Use them to refine and exclude certain contacts from your key segments, rather than as a replacement for proper targeting.

Monitor your metrics: Keep a close eye on key email performance indicators like open rates, click-through rates, unsubscribe rates, and spam complaints. If you see any negative trends, it could be a sign that you need to update or expand your suppression lists.

Putting It All Together

When used strategically, suppression lists are a powerful tool for optimizing your email performance, maintaining a positive sender reputation, and providing a better experience for your contacts. By excluding unengaged, invalid, or ill-fitting contacts from your sends, you can improve your deliverability, engagement, and conversion rates while also staying compliant with key regulations.

Of course, suppression lists are just one piece of the email marketing puzzle. To really maximize your results, you‘ll also want to focus on crafting compelling subject lines and content, personalizing your messages, and continuously testing and optimizing your approach.

But by making suppression list management a key part of your email strategy, you‘ll be well on your way to more efficient, effective, and profitable email marketing. So what are you waiting for? Go forth and suppress!


I hope this guide has given you a solid foundation for understanding the what, why, and how of email suppression lists. By implementing the 7 key types of lists we covered and following email best practices, you can take your email strategy to the next level and drive better results for your business.

Remember – when it comes to email marketing, it‘s not just about reaching the most people. It‘s about reaching the right people with the right message at the right time. Suppression lists are a critical tool for doing just that.

Now get out there and start building those lists! Your sender reputation (and your bottom line) will thank you.