NServiceBus support using interfaces as messages.
Using interfaces to means "multiple inheritance" is supported; i.e., one message can extend multiple other messages. This is useful for solving certain "message evolution" scenarios.
Say that the business logic represents a state machine with states X and Y. When the system gets into state X, it publishes the message
EnteredStateX. When the system gets into state Y, it publishes the message
EnteredStateY. (For more information on how to publish a message, see below.)
In the next version of the system, add a new state Z, which represents the co-existence of both X and Y. So, define the message
EnteredStateZ, which inherits both
When the system publishes
EnteredStateZ, clients subscribed to
EnteredStateY are notified.
Without the ability to extend a message to multiple others, composition would be required, thereby preventing the infrastructure from automatically routing messages to pre-existing subscribers of the composed messages.