For message delivery, SimpleX uses temporary anonymous paired message queue identifiers, separately for each of your connections, instead of the user IDs used by all other platforms – there are no long-term identifiers in it. You define which servers to use to receive messages, and which servers to use to send messages. Each conversation will probably use two different servers.

This design prevents leakage of user metadata at the application level. To further improve privacy and protect your IP address, you can connect to the messaging servers via Tor. User profiles, contacts, and groups are stored only on client devices; messages are sent with two-layer end-to-end encryption.

Even in the most private applications that use Tor v3 services, if you communicate with two different contacts using the same profile, it may be possible to prove that they are connected to the same person. SimpleX protects against these attacks simply and easily by having no user ID in its design. And if you use Incognito mode, you will have a different display name for each contact, preventing data sharing between them. And that's very cool.