No known form of communication can travel faster than light, instead messages are carried by ships moving between systems. By default ships entering a new system download an updated version of relevant information when connecting to the local datasphere, and provide these updates as they travel to other systems.
Because this system is effectively equivalent to a pony postal service, some messages can take quite a while to reach less frequently visited systems. Some out-of-the-way starbases even pay ships just to fly through in order to keep news fresh. Most messages are sent with a degree of encryption, which may need to include a back-door depending on local law, as any given message may bounce around on a half dozen different ships before arriving at the intended destination. On a broader scale major empires, such as the Third Emper’s X-Boat routes, connect between sectors of known space.
Qubit Exchange
Parties wishing to have absolute secrecy in their communications must use expensive and fragile qubits. Entanglement and the No Cloning Theorem ensure that such superdense messages can only be read by their intended recipient.
However each set of entangled pairs only comes as a specific pair between two communicators, and must be delivered physically by a trusted individual to ensure secrecy. Additionally most such messages are hidden inside other communications, as typically governments strongly disallow passing messages through their systems which they cannot, even in theory, read.