Two or more Sophos Email Appliances that are connected on the same network as a group in order to provide centralized management and redundancy.

Each clustered appliance is an independent system that processes messages and provides access to the End User Web Quarantine and the administrative user interface. When clustered, appliances continually communicate with each other. One acts as a configuration manager, coordinating the flow of configuration information between the joined appliances. With the exception of system-specific information (such as hostname and IP address), configuration changes made on one appliance are sent to the configuration manager, which in turn propagates the changes to the other appliances in the cluster.