To ensure Northern Trail Outfitters' sending reputation remains intact, implementing a Sender Authentication Package (SAP) with a Private Domain and a Dedicated IP is the best course of action. This setup provides greater control over the sending environment, allowing the company to build and maintain its sending reputation without being affected by other customers sharing the same domain or IP. It also facilitates the use of SPF, DKIM, and DMARC authentication protocols.
References:
* Salesforce Marketing Cloud Documentation on Sender Authentication Package