Understanding what every message request property contains avoids some time that the developers have to spend when not using the most common message requests (Create, Update). So for that, here below you can find that information that can help sometimes long time on debugging a plugin to discover what we are doing wrong, and it is more a reminder.
Message Request Property Description AssignRequestTargetThe assigned entity.CreateRequestTargetThe created entity.DeleteRequestTargetThe deleted entity.DeliverIncomingEmailRequestEmailIdThe delivered email ID.DeliverPromoteEmailRequestEmailIdThe delivered email ID.ExecuteWorkflowRequestTargetThe workflow entity.MergeRequestTargetThe parent entity, into which the data from the child entity is being merged.MergeRequestSubordinateIdThe child entity that is being merged into the parent entity.SendEmailRequestEmailIdThe sent entity ID.SetStateRequestEntityMonikerThe entity for which the state is set.UpdateRequestTargetThe updated entity.