Identity Resolution Demystified: What is a hashed email?

Email addresses are about so much more than simply sending or receiving digital messages. Consumers use them for everything from signing into their social media accounts, streaming services, and to make online purchases. Emails have become a sort of electronic passport — one that most people keep forever.

It’s easy to see why marketers are so keen on making the most of email addresses. They allow you to identify and engage consumers. But what about when that email is run through the hashing algorithm? 

What is a hashed email?

Initially designed as a security feature, hashed emails are useful identifiers for every marketing channel. The action of hashing means taking a piece of data and converting it to a hexadecimal string. So in this case, that data would be an email address.

Hashing an email means using an algorithm to convert an email address into a cryptographic code. 

Each email is given its own unique hexadecimal string that remains consistent, no matter where the email is used. The email can’t be recognized by a human being, so it’s not personally identifiable information (PII). This action can also not be reversed.

A hashed email is persistent across devices, and you can attach behaviors and information to them in a database or identity graph. That makes hashed emails great people-based identifiers for Internet advertising, as you can easily upload hashed emails into any advertising platform.

Benefits of hashed emails

Here are two of the reasons why hashed emails are so useful:

  • Privacy and accuracy: A hashed email can’t be readily used for mailing, which respects the rights and privacy concerns of consumers. While this practice respects their privacy, it doesn’t sacrifice accuracy in the process.
  • Cross-device communication: The hashed email represents a known customer and remains the same across all devices, apps, and browsers.

Do those benefits remind you of something?

Hashed emails vs. cookies

A hashed email and cookies might sound similar, and that’s because they are in many ways. Let’s take a look at a few of their similarities:

  • Can be used to track behavior across the Internet
  • Data then serves up relevant content across the web
  • For publishers, data can be used to make ad inventories more valuable to brands

However, unlike third-party cookies that can be refreshed or deleted, hashed emails provide a stable ID of a known customer. That means it doesn’t change or get wiped out — and hashed emails remain persistent across all apps, devices, and browsers through time. As we mentioned earlier, they can be loaded into any advertising platform to create custom/lookalike audiences. 

Main hashing functions

A hash function takes a set of inputs of any size and fits them into a table or other data structure that contains fixed-size elements. While all hashes are case sensitive and have no spaces, there are three main functions that are a bit different from one another: 

  • MD5: Message Digest Five algorithm, 32 characters
  • SHA-1: Secure Hash Algorithm One, designed by the National Security Agency; used as a federal information processing standard and contains 40 characters
  • SHA-2: Secure Hash Algorithm Two, SHA-256 is most popular and secure in family, 64 characters, and can be uploaded to Google, Facebook, or anywhere for advertising

The advantage with all of these is that there’s zero PII transferred. Also, you own your audience with these identifiers, unlike with pixels or cookies.

What’s next?

While hashed emails aren’t new, they continue to have staying power by allowing you to obtain data to then create engaging, personalized campaigns without using anyone’s PII.

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