Which feature allows personalization in emails by dynamically populating details?

The feature that allows personalization in emails by dynamically populating details is AMPscript. This scripting language is specifically designed for Salesforce Marketing Cloud, enabling users to create dynamic content within their emails, landing pages, and SMS messages. With AMPscript, marketers can pull in subscriber-specific data from their data extensions, allowing for a tailored experience for each recipient based on their individual preferences, behaviors, and attributes.

Using AMPscript, you can access fields from your data extensions to include personalized elements, such as the subscriber's name or location, directly within the email content. This level of personalization helps increase engagement and relevance, which can lead to higher open rates and improved customer satisfaction.

The other options, while they have their own specific functions, do not directly facilitate the level of dynamic personalization that AMPscript provides. Data Extensions are essential for storing subscriber information, API integrations connect systems for data exchange, and custom HTML tags involve creating design elements in emails but do not inherently provide the dynamic data-driven personalization that AMPscript accomplishes.