End-to-end encryption (E2EE) is a method of secure communication where only the communicating parties can access the data being transmitted, preventing any potential eavesdropping or tampering by intermediaries. In email, end-to-end encryption ensures that the content of emails is encrypted from the sender to the recipient, and can only be decrypted by the recipient with the necessary keys. This provides an additional layer of security beyond traditional email encryption methods.

HIPAA compliant email refers to an email system that meets the security requirements set by the HIPAA regulations. These regulations are designed to protect the privacy and security of electronic protected health information (ePHI) and ensure that it is only accessed by authorized individuals. HIPAA compliant email systems must meet certain technical and administrative requirements, such as encryption of sensitive data, secure transmission of data, and access controls to prevent unauthorized access. They must also comply with standards for privacy and data protection, such as the Health Information Technology for Economic and Clinical Health (HITECH) Act and the Office of the National Coordinator for Health Information Technology (ONC).

End-to-end encrypted email works by encrypting the message content and attachments on the sender's device before it is sent to the recipient, and then decrypting it on the recipient's device with a private key. The encrypted message is transmitted through the email server and any intermediaries, but the contents remain inaccessible without the proper key. The encryption keys are typically generated and managed by the email clients or apps used by the sender and recipient, such as ProtonMail, Tutanota, Signal or Encrypted Spaces. The encrypted email can only be decrypted by the recipient using their private key, ensuring that the contents of the email remain confidential and protected from any unauthorized access.