Server-mediated messaging is a communication model in which messages travel through a provider’s servers before reaching the recipient. Unlike end-to-end encrypted systems, the provider may be able to inspect, route, store, index, or otherwise process message content, depending on the product design and encryption scheme.
This matters in cyber security because the provider becomes part of the trust boundary. Server visibility can help with spam filtering, abuse detection, backups, search, and compliance controls, but it also increases exposure to insider misuse, lawful access requests, data retention risk, and compromise of the provider itself. In attacks, adversaries may target the service backend, administrative tools, or stored message data to harvest conversations. In defenses, teams mitigate that risk with strong access control, audit logging, retention limits, and, where needed, end-to-end encryption that prevents the server from reading the payload.