Explanation
Implementing an SAP with Private Domain and a Dedicated IP is the best action to ensure NTO's sending reputation remains intact, as it allows NTO to have full control over its sender authentication and IP reputation. A private domain enables SPF and DKIM authentication, which helps to verify the sender's identity and prevent spoofing. A dedicated IP isolates NTO's sending volume and reputation from other customers, which reduces the risk of being affected by their sending practices. Requesting three dedicated IPs or a private domain alone would not provide the same level of protection as an SAP.

Explanation/Reference:

A Reference Content Block is a type of content block that allows marketers to reference another content block within an email. This means that any changes made to the referenced content block will automatically update in all emails that use it. A Reference Content Block is useful for including content that changes frequently or needs to be consistent across multiple emails, such as special events or offers.