There are three kinds of message buffers. Outbound and inbound message buffers allow members of groups to communicate with other systems. Outbound message buffers are used to send messages to another system; inbound message buffers are used to receive messages from another system. Local message buffers are used to send and receive messages within the same system.

The various types of message buffers are segregated from one another so that the supply of one type does not affect the supply of any other type. Message buffers used to communicate with one system are segregated from those used to communicate with other systems. Thus, exhausting the supply of message buffers used to communicate with one system does not impact communication with any other system.