Email Hash (SHA-256)

An email hash is a one-way cryptographic transformation of a subscriber's email address. MailAdx uses SHA-256 hashing, which transforms any email address into a fixed-length string (e.g., john@example.com → e3b0c44298fc1c149afb...) in a way that cannot be reversed to recover the original email. Email hashes serve two purposes in newsletter advertising: (1) Privacy — the ad server receives the hash, not the raw email address, so no personally identifiable information (PII) is transmitted in ad request URLs; (2) Identity resolution — the same subscriber across multiple newsletters will always produce the same hash, enabling frequency capping and audience targeting without cookies or device IDs. MailAdx's entire ad serving infrastructure uses SHA-256 email hashes as the only subscriber identifier, making it GDPR-compliant by design.