How Hide My Email Generates Aliases in iOS 15

Apple introduced Hide My Email in iOS 15 as an iCloud+ privacy feature that allows users to create unique, random email addresses to keep their personal email addresses private. This article explains the technical mechanics behind how these randomized aliases are generated, how they interact with Apple's secure infrastructure, and how they seamlessly forward incoming messages to a user's personal inbox without exposing their real identity.

Server-Side Random Generation

When a user requests a new alias in iOS 15—whether through the Settings app, Safari, or the Mail app—the operating system does not generate the email string locally on the device. Instead, the device makes an authenticated API call to Apple's iCloud servers. Apple's backend generates a cryptographically random, alphanumeric string paired with standard Apple domains (primarily @icloud.com).

To prevent user correlation and avoid predictable patterns, the system uses secure pseudo-random number generators (PRNGs). This ensures that two aliases generated by the same user have zero common syntax or mathematical linkage that a third party could use to track them across different platforms.

Integration with Safari and Web Forms

In iOS 15, the generation process is integrated directly into the operating system's AutoFill framework:

  1. Form Detection: Safari detects an email input field on a website or app registration screen.
  2. Key Generation Request: Selecting the "Hide My Email" prompt triggers a background handshake with the iCloud Keychain and Apple ID services.
  3. Database Association: The newly generated alias is permanently mapped in Apple’s internal directory to the user's verified primary Apple ID email address.
  4. Form Injection: The alias is inserted directly into the form field, keeping the user's actual email address isolated from the target service.

The Relay and Forwarding Architecture

The generation of the alias is only the first step; the address functions as a dynamic proxy. When a third party sends a message to the generated alias, Apple's inbound mail transfer agents (MTAs) receive the message, look up the hidden database record associated with that alias, and instantly re-route the message to the user’s designated primary inbox.

For replies, the system reverses this mechanism. When a user responds to a forwarded message from their Mail app, iOS 15 routes the outgoing message through the same private relay architecture. The relay rewrites the sender headers, ensuring the recipient only sees the generated alias rather than the user's personal address.

Local Storage and Revocation Control

Once generated, each alias is stored within the user's iCloud account metadata. iOS 15 displays these aliases under Settings > [User Name] > iCloud > Hide My Email. From this panel, users can label aliases by service, view the specific forwarding destination, toggle forwarding off, or delete the alias entirely. Deleting an alias terminates the server-side mapping, causing Apple's mail servers to immediately reject any future incoming messages sent to that specific address.