Because NTO has explicitly stated it is comfortable sharing digital properties with Cloud Kicks and intends to actively associate its own brand with the new subsidiary during a coordinated launch campaign, applying a Private Domain scoped to the Cloud Kicks child business unit is the appropriate, lighter-weight solution: it gives Cloud Kicks its own custom sending domain for links and tracking while still allowing the association between the two brands to be visible and intentional, and it can inherit and benefit from the parent NTO domain ' s already-established sender reputation, which is advantageous given deliverability is a stated primary concern for a new sender with only moderate monthly volume (50,000/month). A brand-new, fully independent Sender Authentication Package for Cloud Kicks (C) would require building sender reputation entirely from scratch, a materially higher deliverability risk for a new, moderate-volume sender than leveraging an established parent domain ' s reputation through a Private Domain relationship. Option B, a new SAP for NTO itself, doesn ' t address Cloud Kicks ' need for its own custom sending identity at all. Option A misapplies the Private Domain at the parent level rather than scoping it to the child BU that actually needs the custom domain. Reference: Private Domains, Sender Reputation for New Senders.