Identity mapping is the internal link between an outward-facing alias and the real account, mailbox, or user record behind it. In email privacy systems, the alias is what senders see, while the mapping tells the service where messages should actually be delivered. This hidden association is what makes forwarding, account recovery, and routing possible.
In cyber security, identity mapping matters because it is often the privacy boundary itself. If the mapping is exposed through a bug, weak access control, logging mistake, or rendering error, an attacker may learn the real address behind a protected alias. That can lead to deanonymization, targeted phishing, spam, or account correlation across services. Defenders protect identity mappings with strict separation, least-privilege access, careful validation, and testing of every lookup and forwarding path so the alias layer does not leak the identity underneath.