Message Id strategy

Component: RabbitMQ Transport
NuGet Package NServiceBus.RabbitMQ (4.x)
Target NServiceBus Version: 6.x

By default, the message-id property of the AMQP standard is used to relay the message identity. If this header isn't set, the transport will throw an exception because NServiceBus requires a message identity to perform retries, de-duplication, etc., in a safe way. For integration scenarios where the sender is not controlled, consider using a custom scheme that extracts a message identity from a custom header or some data contained in the actual message body. This custom strategy can be configured by calling:

var transport = endpointConfiguration.UseTransport<RabbitMQTransport>();
    customIdStrategy: deliveryArgs =>
        var headers = deliveryArgs.BasicProperties.Headers;
        return headers["MyCustomId"].ToString();
It is extremely important to use a uniquely identifying property of the message in a custom message identity strategy. If the value for a message were to change (for example, if attempting to use Guid.NewGuid().ToString()) then message retries would break, as the infrastructure would be unable to determine that it was processing the same message repeatedly.

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