What is Email Hashing? The Importance of Hashed Email for Future Success


With the cookieless future set to arrive now in 2023—when Chrome (and 60% of the browser market) will join Safari and Firefox in blocking third-party cookies—hashed emails (HEMs) are gaining importance as a key identifier, and for good reasons. 

For one, they act as a ‘key’ on identity maps which can help marketers link customer behaviors across devices, channels and platforms, while still preserving user privacy. But also because HEMs are more effective than third-party cookies in powering data-driven advertising on new channels like CTV, streaming and digital TV, which rely on email sign-on models. HEMs provide a truly scalable way to connect online data to connected TV advertising, the fastest growing area of video advertising, for better targeting

A HEM By Any Other Name Is Still an Identifier

While HEMs are the ‘something old’ of the targeting world, they’re coming into their own as devices, channels and platforms proliferate in our digital world. 

Very simply, an email hash is a computer programming tool: a 32-character code that is unique to a given email address through a process of pseudonymization. The result is an identifier that can be used to securely authenticate a web browser for transactional or other purposes, such as tracking and targeting across multiple devices and over a sustained period of time for upper funnel, and other, marketing purposes. 

An email has is a 32-character code that is unique to a given email address through a process of pseudonymization

Similar to mobile ad IDs (MAIDs) or Android ad IDs (ADIDs), hashed emails can be reversed if a user has the decryption key, and thus are considered personal identifiable information (PII) subject to GDPR requirements. Technology and data collection measures can also be used to link multiple HEMs, MAIDs and ADIDs, for those individuals with more than one email or device, to resolve digital identities across platforms and devices. 

Nope, Hashed Emails Are Not All the Same 

There are different types of hashed algorithms, for example: MD5, SHA-1, SHA-2, SHA-256,  and even SHA-384. They each produce different hash values. For example MD5, short for Message-Digest Algorithm 5, produces a 128-bit hash value, while SHA-1 produces a 160-bit hash value. SHA-256 produces a 256-bit hash value, etc. The longer the hash value, the greater the performance hit for processing time. For our purposes, the fundamental differences of these algorithms is their encryption level, or cryptographic security. (SHA stands for Secure Hash Algorithm, with the number indicating the level of encryption applied.)

While some insecurities have been identified with MD5, it’s still considered the most commonly used hashing algorithm for verifying file integrity. In cryptography, it’s used in security protocols such as Secure Shell (SSH), Secure Socket Layer (SSL), and Internet Protocol Security (IPSec). So widespread is its use that some applications strengthen the MD5 algorithm by adding a salt value to the plaintext or by applying the hash function multiple times.

Two types of hashed algorithms are MD5 and SHA, while the former is more widely used the latter is more secure

HEMs Are Handy for Marketers

Emails are ‘universal’ or ‘central’ IDs we all use with our average U.S. household’s 10 connected devices every day. For the multichannel marketer, HEMs derived from those emails are a cross-channel, target behavior goldmine going far beyond MAIDs and ADIDs. But that’s just the beginning. 

More than half of respondents in a 2015 DMA survey reported keeping core email accounts for at least 10 years, the same length of time as a U.S. Passport. The comparison is apt, considering that HEMs offer marketers an identifier that is stable across time as well as devices and platforms. In short, hashed emails allow marketers to tag along, across channels, platforms and devices to every logged-in action your customer or target takes—literally for decades. 

This makes a huge difference to digital marketers. Categorized as Over The Top (OTT) by the Interactive Advertising Bureau (IAB), CTV is the fastest growing area of video advertising. When combined with streaming and digital TV in a media plan, CTV approaches the kind of massive scale associated with traditional TV. [Read more about CTV.] Adding HEMs to the identity map adds the depth of data that can deliver quality results at scale. 

The average American had access to more than 10 connected devices in their household in 2020

Are Your HEMs Ready? Moving Forward Proactively

Without third-party cookies, marketers would be well-advised to combine a customer’s hashed emails with the brand’s or advertiser’s corresponding first-party cookies to view online activity over time and across platforms and devices to enhance campaign performance. 

Other third-party data can also be used with HEMs to augment campaign targeting and performance. Data from offline interactions such as desk agents, call centers, and walk-in encounters can be made available through CRM systems and other integrations. 

Industry tech leaders, like Infutor, offer a variety of data collection, aggregation and analysis capabilities such as adding multiple MAIDs/ADIDs, hashed emails and demographics per digital identity to enhance match rates and improve personalization across channels. New initiatives are also in process from major tech players including The Trade Desk, LiveRamp and Xandr, among others, as well as identity-free targeting through new machine learning models. 

All these efforts offer a range of data sources to replace third-party cookies and help marketers continue to develop addressable targeting. Further, programmatic targeting needs can be met with an array of keywords, categories, search engine marketing, and metasearch to expand contextual targeting options. 

Key Takeaways

While not a new technology, nor free from GDPR, HEMs offer marketers a new superpower: the ability to connect targeting data across all the devices, platforms, and channels to which an email has access for the lifespan of that email – on average 10 years. You might say the demise of third-party cookies offers marketers unprecedented opportunity.

At ShareThis, we’re increasingly leveraging HEM’s as an identity key for our data solutions, with rapidly growing HEM coverage across our data set. Our HEM-based Audience Segments can be used right now for programmatic targeting, from display to CTV campaigns.

About ShareThis

ShareThis has unlocked the power of global digital behavior by synthesizing social share, interest, and intent data since 2007. Powered by consumer behavior on over three million global domains, ShareThis observes real-time actions from real people on real digital destinations.

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