HEMs and Identifiers: How Identity Signals Increase CPMs

In our first post, we introduced bid enrichment as the process of improving the signal associated with each impression before it enters the auction. Now we’re going one level deeper into how that enrichment happens, starting with alternate identifiers and hashed emails (HEMs).

When buyers evaluate impressions in the open market, what they’re really trying to understand the user behind them, alongside the context and quality of the impression. For a long time, that understanding was driven by cookies. As cookies have become less reliable, and in many cases unavailable, that signal has started to break down.

What’s replaced it isn’t a single solution, but a shift in how user signals are built and interpreted. Today, buyers rely on a mix of signals to understand who they’re reaching and how valuable an impression might be. At a high level, those signals fall into two categories: probabilistic and deterministic.

How Buyers Understand Users in the Auction

Probabilistic: A Best Guess

Probabilistic signals are built on inference. A buyer might look at the content of the page, the device, or behavioral patterns and use that information to estimate who the user might be.

This approach has been a core part of programmatic for years, and it still plays an important role, especially where identity signals are limited. But it’s built on probability. Buyers are forming a view of the user, not recognizing them outright.

Deterministic: Known, Not Assumed

Deterministic signals work differently. Instead of inferring who the user might be, they allow a buyer to recognize the user based on a known signal, something they can match directly to their own data. There’s less guesswork involved. That can change how confidently a buyer makes a decision. 

If buyers can match that signal to their own data, they move closer to knowing that user.  And that higher degree of certainty shows up in how they bid: often with more confidence, greater willingness to compete, and in many cases, higher CPMs.

What Are Identifiers in Programmatic Advertising

Identifiers are how that understanding gets carried into the auction, privacy-safe signals that help buyers recognize a user and decide what that impression is worth.. They connect the impression to buyer data, giving DSPs a way to recognize users, apply targeting, and decide how much that impression is worth.

You’ll see this through IDs like UID2, ID5, RampID, Yahoo ConnectID, Criteo ID, and others. These are signals buyers use to recognise and target users within the impression. But it’s not about having one identifier; it’s about coverage. 

Different buyers rely on different IDs. Different environments support them differently. And what works for one audience won’t necessarily translate to another. From a publisher’s perspective, you don’t need to know which ID matters most to which buyer. What matters is making your impressions as addressable as possible across the board.

Because when more buyers can recognize a user:

• more of them can act on the impression
• more of them compete
• and pricing improves

Publishers don’t need to pick the winning ID. They need to make sure they’re not missing demand because the right signal wasn’t there.

How HEMs Strengthen Identity Signals

A hashed email (HEM) is a privacy-safe, encrypted version of a user’s email address. It doesn’t expose personal information, but it provides something far more valuable: a stable signal that can be recognized across environments. That stability is what changes how an impression is valued.

A HEM allows buyers to:

• recognize the user with confidence
• connect the impression to their own data
• apply identifiers more consistently across the auction

You’ll often see it working alongside identifiers like UID2, RampID, and others, but its role is more foundational than that. It often acts as the input that seeds these identity frameworks, allowing them to generate or map identifiers more reliably. It’s not the only way identifiers are generated. But it’s one of the most reliable inputs available, especially in environments where cookies don’t exist, like Safari and iOS.

Without a strong input signal, identity becomes fragmented. Match rates vary. Buyers miss opportunities to recognize users they would otherwise value. With a HEM in place, that signal holds. More impressions can be understood, and more buyers have the opportunity to act on them.  

From a publisher’s perspective, the shift is straightforward: When buyers understand the user, they price the impression as more valuable. 

Across the Adapex network, that difference has been  measurable:

• Impressions delivered to users with an established HEM generate 17%–25% higher CPMs
• The observed average lift is +21%

This isn’t tied to a single buyer or ID framework. It reflects broader demand behavior: more confident bidding, stronger competition, and more consistent pricing. You don’t need perfect coverage. But the more of your inventory that carries a signal buyers can recognize and use, the more consistently it’s valued for what it actually is.

What This Means for Publishers

This isn’t about changing your site experience or increasing ad density. It’s about making each impression more understandable and therefore more valuable to buyers.

At typical levels of HEM coverage, that translates to:

• +10%+ revenue lift on existing inventory

No additional traffic. No new placements. The audience is already there. The difference is how clearly that audience shows up in the bid request.

The Takeaway

Identity isn’t a checkbox. It’s a spectrum, from inferred signals to known users, and where your impressions fall on that spectrum directly impacts revenue. Identifiers help carry that signal. HEMs strengthen it.

Across the Adapex network, impressions with a HEM command materially higher CPMs because buyers can recognize, match, and act on them with confidence. We’ve seen this consistently across real publisher environments, not modeled, not assumed.

The more of your inventory that can be clearly understood in the auction, the more consistently it will be valued correctly. Clarity drives competition. Competition drives revenue.

In the next post, we’ll look at the other side of the signal, context, and how it shapes value in the auction.