Data Retention Policies in Salesforce Marketing Cloud allow youto automatically manage the retention and deletion of data within data extensions. This feature can be configured to delete records after a specified period, such as 30 days, ensuring that non-registered customer information is automatically removed in compliance with data management policies.
Reference:Salesforce Marketing Cloud Documentation on Data Retention Policies

Reference:Salesforce Documentation - Path Optimizer

Einstein Content Selection uses AI to automatically select and deliver the most relevant content to each subscriber, increasing engagementand click rates. For Northern Trail Outfitters, this feature can help personalize holiday promotional emails based on individual subscriber engagement. More information can be found in theEinstein Content Selection documentation.

Subject and Preheader Validation is a feature in Salesforce Marketing Cloud that checks for common issues in the subject line and preheader text before an email is sent. This validation would alert users to potential problems, such as placeholder text like "[For APPROVAL]", helping to avoid sending emails with incorrect subject lines.
Reference:Salesforce Marketing Cloud Documentation on Subject and Preheader Validation

To address the increase in unsubscribes without eliminating planned emails, the marketer should use a Frequency Split. The Frequency Split activity in Journey Builder helps marketers segment their audience based on how frequently they want to receive emails. By focusing on subscribers who are least likely to unsubscribe, the marketer can continue their email campaigns while reducing the risk of further unsubscribes.
Reference: Salesforce Marketing Cloud Documentation on Frequency Split in Journey Builder