What is Blacklist?
Also known as: Block list, Exclusion list, Deny list
What is a blacklist?
A blacklist is a list of domains, apps, IP addresses, or keywords that a system blocks from a specific action. In digital advertising, the blacklist tells an ad platform where ads must not appear. In email, it tells a mail server which senders to refuse.
The principle is the same across both. Block by default for anything on the list. Allow everything else. This makes a blacklist an exclusion-based control, the opposite of a whitelist, which allows only what is on the list.
Blacklists answer four operational questions:
- Which placements waste budget?
- Which domains carry brand-safety risk?
- Which IPs or domains send spam?
- Which search queries should never trigger our ads?
Get the list right and your campaigns stop bleeding into the wrong inventory.
How a blacklist works
Different platforms apply blacklists at different points in the request flow. The mechanics are simple. The data behind them is not.
Programmatic placement blacklists
Inside a demand-side platform (DSP), the blacklist sits at the bidder. When an SSP sends a bid request for an impression on example.com/article, the DSP checks the domain against the campaign's exclusion list. If it matches, the DSP skips the bid. If it does not match, the auction proceeds.
The list usually contains:
- Domains.
clickbait-news.com, scraper sites, MFA (made-for-advertising) inventory. - App bundle IDs. Specific iOS or Android app identifiers known for fraud or low quality.
- Placement IDs. A specific ad slot inside an otherwise-acceptable site.
- Categories. IAB content categories like adult, hate speech, or violence.
The IAB Tech Lab ads.txt and app-ads.txt specifications give buyers a way to verify that the seller actually has the right to sell that inventory. Lists generated from ads.txt mismatches are a common starting point for any blacklist.
Email blacklists
Real-time blackhole lists (RBLs) work differently. Mail servers query a public DNS-based list when they receive incoming mail. The classic example is Spamhaus, which publishes the SBL (Spamhaus Block List) and XBL (Exploits Block List). If the sending IP appears, the receiving server can reject, defer, or quarantine the mail.
According to Statista, spam represented around 45.6 percent of global email traffic in 2023. Without blacklists, inboxes would be unusable.
Keyword blacklists in paid search
In Google Ads and Microsoft Ads, a keyword blacklist is implemented as a negative keyword list. The platform compares each search query against the negatives. If a query matches, your ad does not enter the auction. This is how ecommerce advertisers stop paying for "free," "cheap," or competitor brand terms.
Why blacklists matter
A blacklist is the cheapest brand-safety control an advertiser has. Three concrete impacts:
- Lower waste. Sites with high bounce, low viewability, or invalid traffic burn budget. Adding them to the exclusion list redirects spend to inventory that converts. The Association of National Advertisers found in 2023 that 23 percent of programmatic media spend was wasted on fraud, MFA, and unviewable inventory. Blacklists are the first lever that closes that gap.
- Brand safety. Ads next to extremist content, pirated streams, or misinformation create reputational risk. The GARM Brand Safety Floor defines categories like adult, illegal drugs, and hate speech that most advertisers blacklist by default.
- Compliance. Regulated verticals (pharma, finance, gambling) have legal exclusions. A blacklist enforces them without manual review on every impression.
Real-world example: cleaning up a programmatic campaign
A mid-market DTC apparel brand runs a programmatic display campaign on a major DSP. Monthly spend is $75,000. CPM is $3.40. The campaign generates 22 million impressions a month and a CPA of $48.
A 30-day placement audit reveals that 18 percent of impressions are served on 412 low-quality MFA domains. These placements have a click-through rate of 0.03 percent and a post-click conversion rate near zero.
The team builds a domain blacklist from three sources:
- The 412 MFA domains identified in the audit.
- The Jounce Media MFA list (publicly maintained, updated weekly).
- Domains flagged by their IAS pre-bid verification.
The exclusion list goes live with 1,800 domains. Over the next 30 days, the same $75,000 buys 18.4 million impressions instead of 22 million. CPA falls from $48 to $34. Total conversions rise by 24 percent because the freed budget moves to inventory that actually performs.
The blacklist did not save money. It moved the same money to better inventory.
Blacklists in an AI ad platform
In a connected ad-creation-and-launch platform like Coinis, blacklist management is automated where it can be and surfaced where it cannot.
When a campaign launches into Meta or programmatic channels, the platform applies a default exclusion list built from publicly known fraud sources, GARM-flagged categories, and competitor brand terms. The marketer never opens an SSP dashboard to upload a CSV.
After the campaign runs, the platform watches for placements with statistically poor performance: high spend, low CTR, zero conversions. These get flagged for one-click addition to the campaign's exclusion list. The blacklist grows as the data grows.
The same logic applies to negative keywords on search campaigns and to retargeting audiences that should never see prospecting creative. The list does the work. The marketer reviews the deltas.
A clean blacklist is not a one-time project. It is an ongoing input to every campaign decision. Automating the boring parts means the manual review focuses on the calls only a human should make.
Related terms
Frequently asked questions
What is the difference between a blacklist and a whitelist?
A blacklist blocks specific items and allows everything else. A whitelist does the opposite. It allows only the items on the list and blocks everything else. Whitelists are stricter, safer, and more expensive to maintain. Blacklists scale better but let new bad actors slip through until they get reported.
How do programmatic ad blacklists work?
Inside a DSP, you upload or build a list of domains, app bundle IDs, or placement IDs. Before the DSP bids on an impression, it checks the placement against the list. If the placement is on the blacklist, the DSP skips the bid. The same impression then goes to another buyer.
What is an email blacklist?
An email blacklist is a public registry of IP addresses or domains that have sent spam, malware, or phishing. Receiving servers check incoming mail against blacklists like Spamhaus SBL, Barracuda, or Spamcop. If the sender is listed, the mail is rejected or routed to spam. Roughly 45.6 percent of all email traffic was spam in 2023 according to Statista.
How do you get off an email blacklist?
Find which list flagged you using a tool like MXToolbox. Visit the blacklist provider's removal page. Spamhaus, Barracuda, and Spamcop each run their own form. Fix the underlying issue first (compromised account, missing SPF or DKIM, list hygiene). Submit the delisting request. Most providers respond within 24 to 72 hours.
Are blacklists still effective with modern ad fraud?
Yes, but they are not enough on their own. Static blacklists miss new fraudulent domains until someone reports them. Modern brand safety pairs a blacklist with real-time verification from vendors like IAS, DoubleVerify, or HUMAN. The blacklist catches known offenders. The verification layer catches new ones in flight.