It has happened to nearly everyone who owns a smartphone or a computer: the dreaded email or targeted advertisement that contains content that is irrelevant to your needs. This often leaves you, the end user, annoyed and left with a bitter taste for the company responsible for the advertisement. According to, “67% of customers say brands need to automatically adjust their content based on a customer’s current context. And 42% say they get annoyed when content isn’t personalized.” This annoyance leads to higher than average unsubscribe rates, low engagement, wasted advertisement dollars, and potential customer resentment. To avoid this, marketers need to establish a list suppression strategy that is equally important to the overall targeted communication strategy.

What is a Suppression List?

First, let’s define what a suppression list is. A list of contacts that are removed from all or specific marketing campaigns for reasons that include, but are not limited to:

  • Unsubscribed
  • Spam compliant
  • Non-deliverable email address
  • Non-deliverable domain
  • Content irrelevancy

Let’s do a deeper dive to define what these all mean by separating out basic suppression types versus advanced suppression types.

Basic Suppression Types

There are many reasons why a contact will unsubscribe, but the important thing to note is this must be respected to avoid lawsuits or financial penalties. Nearly all email platforms will process unsubscribes the same way, by automatically applying a unsubscribe field designation that tells the platform to remove the unsubscribed contact from all future email communications immediately.

Spam Compliant

A spam compliant is generally a function within the users email platform that allows them to flag an email sent to them as spam. If there are too many spam complaints from the same sender then the ESP (email service provider) has the ability to provide a negative reputation score to the sending domain, that will ultimately affect future email sends by routing those emails to a junk folder or spam traps that will never end up in the user’s inbox. All spam complaints should be treated very similarly as unsubscribes, and should be removed from future email sends to avoid any negative reputation scoring.

Non-Deliverable Email Address

A non-deliverable email address is an address where the characters before the @ are either no longer valid due to the account being turned off or deleted, or the characters were entered wrong as it entered the database.

Non-Deliverable Domain

A non-deliverable domain generally means the business you are sending to is no longer in business and is no longer receiving emails to any address with the domain of the address. Be sure to check spelling, as this may also be a cause to this issue.


Advanced Suppression Types


Frequency is one of the rarer types of suppression that involves a voluntary user preference form that tells your automation system how often the user would like to be contacted in any given timeframe. This essentially allows the user to decide the frequency in which they receive content. For those looking for constant communication, they can notify the system that’s what they are looking for. This typically works well for businesses who offer daily deals where they want to let their database know what deals they currently have running. For someone who is only somewhat interested in their products wouldn’t want an email from them every single day as that would become tiresome and therefore would remove its effectiveness.

Product specific

If you have specific product or service type related emails, a user could choose to receive emails that are specific to the product or service they own. They would then be opted out of any other products or services emails that you may offer. For example, an HVAC company that sells and installs a variety of different brands of air conditioning units just completed an install of a TRANE® unit on a customer’s home. This customer should then be placed into a TRANE® customer list and immediately suppressed from all other similar product lists to avoid a potential unsubscribe or spam compliant. All AC unit communication to this customer going forward should be specific to their TRANE® unit.

Content Type

In many cases, your organization may have multiple different types of content that are sent out to your customer base. This could include content types such as weekly newsletters, daily deals, anniversaries, transactional support, geographic specific, demographic specific, or seasonal communication. Creating different buckets for each of these types and suppressing contacts that don’t belong will go a long way in your overall communication strategy as you work to create highly targeted messages within each bucket.

In-Active Subscribers

One of the ways to help improve your overall open and click rates is to establish an In-active suppression list. The length of your sales cycle will determine the timeframe that you consider in-active for you and your organization. In many cases I have seen this be anywhere between six months to two years for which the cutoff point should be set. Fields that should be considered in your logic include, but are not limited to:

  • The last time an email was opened/clicked
  • The last time a customer has made a purchase
  • The last time the user has visited the website
  • CRM data, such as last time your sales rep has contacted the customer either by phone or email.

I highly encourage these lists to include more than one piece of criteria so that you can be sure that you are querying a more precise in-active list. Hot tip: make sure your criteria also includes a contact creation date so that your list doesn’t include newly added contacts that haven’t been given the opportunity to become active yet.


Expert Level Suppression – Customer Data Platform (CDP)

Today your customers are shopping on many devices and platforms that add to the complexity of knowing “who is who” when a purchase occurs. This makes things extremely difficult when properly attributing credit to your marketing campaigns. With the use of a CDP, you can collect all tracking pixels and customer data under one roof to provide your team a single accurate and holistic view of your customer database. With this capability, you can create expert level suppression strategies that support a unique customer experience across all platforms and devices.

For example, you have a customer that places a product in their online shopping cart and doesn’t immediately complete the purchase. To help increase your conversions you have established a retargeting campaign to bring users back to their shopping cart to complete their purchase. Along with this, you also have an email abandon cart campaign sending a series of emails to the known customer about the item they have left in their cart. A few short days later the customer returns to their cart on a different device and completes their purchase. Your email tool is able to acknowledge a purchase has been made and removes the customer from the abandon cart campaign, but because the purchase was completed on a different device from the initial abandon cart the customer will still be receiving retargeting ads on the product they have abandoned.

With the use of visitor stitching through a CDP, the technology is then able to identify the identity of both devices and merge both sessions into one holistic user profile to complete a clear picture of who your customer is. The CDP then sends this data to the retargeting tool to let it know this customer has completed a purchase from their abandoned cart, and that they should be placed on a suppression list which will then remove them from the retargeting campaign in real time. The ability to place customers on suppression lists based on data from other platforms helps to create a true 1:1 digital customer experience.


In summary, suppression types can be used in a multitude of different ways, and each comes with its own importance. As important as it is to strategically target you should be talking to, you should also equally strategic when it comes to who you should not be talking too. Using a combination of the two will surely provide positive results as you look to increase conversation rates and overall customer satisfaction.