For Northern Trail Outfitters to avoid storing sensitive information such as email addresses and phone numbers directly in Marketing Cloud, the recommended feature is:
Tokenized Sending: This method replaces sensitive data with tokens that can be used in communications without exposing actual data values. It helps in maintaining the confidentiality and integrity of personal data while still enabling personalized marketing communications.
Implementation: Set up Tokenized Sending by configuring the data relationships either through Marketing Cloud Connect or using an external token provider. This ensures that during the send process, the system uses tokens to retrieve and incorporate actual data temporarily without storing it in the database.
Reference: Salesforce Marketing Cloud Tokenized Sending

When Northern Trail Outfitters imported a file into All Subscribers and received a results file indicating that [email protected] could not be imported, the likely error code that would appear in the file is B. List Detective. List Detective is a built-in functionality of Marketing Cloud that prevents the addition of email addresses that do not meet certain criteria to ensure list quality and compliance. It automatically blocks common role-based emails or improperly formatted email addresses.
Reference: Salesforce Help - List Detective

For linking demographic information to a contact model in Contact Builder:
A). One-to-Many Relationship: This type of relationship is appropriate when a single contact can have multiple demographic records. It helps to manage and utilize demographic data effectively within personalized marketing campaigns.
This relationship type supports efficient data management and targeting by allowing multiple demographic attributes for a single contact within the marketing database.
Reference: Salesforce Help - Data Relationships in Contact Builder

In Salesforce Marketing Cloud, linking new data extensions in Data Designer to existing contact records requires using a "Unique Contact Identifier." This identifier ensures that each record in the data extension can be uniquely associated with a corresponding record in the contact database, thereby enabling accurate targeting, segmentation, and personalization. It is vital that this identifier is consistently used across data extensions to maintain data integrity and proper linkages.
Reference: https://help.salesforce.com/

To verify if a Sender Authentication Package (SAP) has been set up, check:
Tracked Links Prefix: If all links in emails sent start with click.email.nto.com, it indicates that a SAP is configured for link rewriting to include the company's domain.
CloudPages URL: Personalized URLs for CloudPages that use the domain cloud.email.nto.com also suggest that SAP is set up, ensuring that all customer-facing URLs reflect the organization's branding.
Reference: Salesforce Marketing Cloud SAP Documentation