What is a Blocklist/Allowlist, and Should You Have One?

If you’ve ever wondered, what is a blocklist and is having one worth it, then let this blog post be your guiding light. Here, we will provide some basic overviews and cover the top-level arguments for and against this strategy. 

What is a Blocklist in Advertising? 

A blocklist is a list that details where a brand or agency categorically does not want their ads to appear, for any number of reasons but often mostly because of brand safety or fraud concerns.  

On the flip side of a blocklist is an allowlist, where a brand or agency is saying that they are okay with their ads appearing only on select apps or websites. This approach originated in telemarketing and email marketing, with marketers only sending communications to select email addresses or IP addresses. 

What are the Pros and Cons and Blocklists/Allowlists? 

Blocklists and allowlists are most often implemented for three key reasons: to ensure brand safe placements, to mitigate potential fraud and/or to ensure legal compliance.  

• Many of today’s advertisers are worried that their brand will be negatively impacted if their advertising appears alongside content that does not align with the brand’s values. For example, if a brand’s ad appears next to a news article about violence, some consumers would be turned off with the implicit takeaway that the brand condones the violence. To ensure these kinds of issues don’t arise, many brands implement blocklists to ensure their ads don’t appear on websites or apps where these kinds of issues are most likely to arise, like on politically charged platforms. Similarly, others will use allowlists to ensure their ads only appear in places where the brand or agency knows that these kinds of issues unlike to arise, like in a casual gaming app. 
• Some websites or apps have developed a reputation as being spam traps where fraud is more likely to occur. Both blocklists and allowlists can thus help advertisers avoid being implicated with the more common sources of spam or fraud. 
• For legal reasons, brands may want to avoid advertising on certain sites or apps. After all, an alcohol brand would want to avoid running ads with publishers whose primary audience are people under the legal drinking age. Considering that the fines associated with running afoul of these kinds of laws and legal frameworks can be quite steep, having a blocklist or allowlist in place to ensure compliance is key. 

Still, like any other marketing tactic, there are potential downsides to blocklists and allowlists that brands and agencies need to keep in mind. 

• Blocklists on their own are often not sufficient to block all potentially hazardous apps or websites, as these properties can appear and multiply before they can be added to a blocklist. With blocklists in place that are not updated frequently, brands are constantly playing whack-a-mole with fraudsters. 
• Allowlists on the other hand can severely limit scale and reach for advertisers. This is especially the case when the allowlists are too restrictive, often because they do not reflect current market realities. For example, some brands avoid advertising on mobile gaming apps under the mistaken assumption that they are rife with violence or don’t have the right audience, even though neither of which is true in today’s casual gaming environment. 
• Maintaining blocklists and allowlists can be quite cumbersome and labor intensive, requiring marketers to constantly audit their lists and the programmatic environment to stay ahead of potential issues without throttling reach too much. 

For many brands and agencies, however, it’s not an either/or situation. Often, the strategy is to constantly maintain both blocklists and allowlists while also working with additional tools or vendors to ensure maximum reach and to prevent any issues from slipping through the cracks.