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People don't have email addresses in their contact lists because all their email contacts are stored on Google servers.

• xorcist 4y ago
  Having the ability to identify by other strings than "phone number" wouldn't take away any functionality, just add it. It would be possible to communicate with devices that have email but not phone numbers (children without SIM cards, for example). But this is all moot because phone numbers aren't just opaque binary strings. They are more useful than other forms of identification.
  • spullara 4y ago
    That isn't why Signal uses phone numbers. It uses phone numbers because users have a local list of phone numbers they communicate with and Signal can use that to determine if people you communicate with are on Signal. If there was a reliable local list of email addresses they could use that but most people use cloud email now and don't have their email addresses they communicate with on their device.