Abstract: A messaging system uses a relational model to represent messages exchanged among end-users of the system. A message within the system contains one or more submessages. A contents module stores data describing the content of each message and submessage. An attributes module describes the attributes possessed by the messages and submessages. A relationships module describes the relationships among the messages and submessages. Because submessages are separate from the messages that contain them, different policies can be applied to individual submessages. Moreover, the messaging system stores each object (e.g., message or submessage) only once. The messaging system thus significantly reduces infrastructure costs by removing unnecessary duplicity, and provides enterprises with the content granularity they need to enforce regulatory compliance and other policies.