Message attributes

Additional metadata can be added to any type of message as attributes alongside the actual message.

When sending via a transport (eg: SQS, RabbitMQ) the message is sent in a message envelope. Commands and events are serialized into the message body, whilst attributes are added to the message header.

Attributes are designed to hold data that is related to technical concerns of routing the message, or auditing/logging information such as details around the originator.