envelope.cs

public class Envelope<T> : IAsyncRequest, IAsyncNotification
{
    public Envelope(Guid messageId, Guid correlationId, T message)
    {
        MessageId = messageId;
        CorrelationId = correlationId;
        Body = message;
    }

    public Envelope(T message) : this(Guid.NewGuid(), Guid.NewGuid(), message) { }
    public Envelope(Guid correlationId, T message) : this(Guid.NewGuid(), correlationId, message) { }

    public T Body { get; }
    public Guid MessageId { get; }
    public Guid CorrelationId { get; }
}