A communication system has a plurality of collections. Each collection comprises a security boundary within which private data is accessible. Each collection is associated with a director. The directors receive messages that specify domains. When a director for a given collection receives a message, the director identifies one of the collections as being a home collection for the domain specified by the message. If the specified domain's home collection is the given collection or another collection within a given privacy boundary, the director forwards the message to a server pool associated with the specified domain's home collection. Otherwise, if the specified domain's home collection is not within the given privacy boundary, the director forwards the message to the director of the specified domain's home collection.