* The Shipment object requires a Lookup to Lead or Contact1. This is because triggered sends can only be sent to Salesforce contacts, leads, or person accounts when object records are created or updated1.
* An Apex Trigger is created on the Shipment object2. This is because a trigger is Apex code that executes before or after certain operations on an object2, and it can be used to invoke the Marketing Cloud integration action that triggers the email send3.