The way Loopix works is very similar to Tor, both being based on the same principles of mix networks. A user connects to a provider (ingress provider), the same way Tor users connect to entry guards.
The Loopix provider server sends the user’s message through the network through random mix nodes, similar to how Tor sends messages through relays.
The message arrives at the intended user’s provider (egress provider), where it is stored inside a message box until the user comes online. This is where Loopix is different, allowing the storage of offline messages.