Glossary/Privacy and identity/Hashed email
What is a hashed email and how is it used in advertising?
How email hashing works, why it is used for audience matching, and why it is still personal data under GDPR.
Written by Samhub with the help of AI·Updated 13 Oct 2026·3 min readA hashed email is an email address run through a hash function, such as SHA-256, that turns it into a fixed string of characters. The same email always gives the same hash.
How it works
Normalize
Lowercase and trim the address.
Hash
Run it through SHA-256.
Match
Two parties compare hashes instead of emails.
Where it is used
| Use | Example |
|---|---|
| Universal IDs | IDs built from logged-in readers‘ emails |
| Clean rooms | Matching a retailer‘s and a publisher’s customers |
| Customer lists | Reaching known customers on a platform |
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Still personal data
Hashing is pseudonymization, not anonymization. Anyone with the original email can create the same hash, so GDPR still applies and a legal basis is needed.
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Frequently asked questions
Not directly, but known emails can be hashed and compared.
No. It is pseudonymized personal data.
SHA-256 is the most common in advertising.
So that “Anna@x.se” and “anna@x.se ” give the same hash.
Related terms
Replacing direct identifiers so data cannot be linked to a person on its own.
A shared identifier that can replace third-party cookies.
Lets two parties match data without sharing it.
Readers who are signed in to your site or app.
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