Verification Activity is the step that prevents the automation from completing the automation instance and delivering an inaccurate report if some agents have not created their data extensions in time. This activity verifies that a data extension meets certain criteria, such as row count or field value, before proceeding to the next step. If the criteria are not met, the activity stops the automation and sends an email notification. Data Extract Activity is a step that extracts data from a data extension or data view and places it in a file on the Enhanced FTP server. Wait Activity is a step that pauses an automation for a specified period of time.

Overwrite is the best import option to ensure the data extension only contains currently active customers, as it deletes all existing records in the data extension and replaces them with the new records from the import file.
This ensures that only customers who are included in the daily feed remain in the data extension. Append or Add and Update would not work for this scenario, as they would either add new records without deleting old ones or update existing records without deleting old ones.

Triggered Automation is a feature that allows marketers to run an automation when a file is dropped into a specified location, such as an FTP folder or Enhanced FTP folder. Triggered Automation can accommodate the setup of NTO's third-party point-of-sale software that sends order information in batches of large files at varying times throughout the day. [Source: Trailhead]

The DoNotTrack attribute is a personalization string that can be used to prevent Marketing Cloud from tracking opens and clicks for a specific subscriber. It can be set to true or false in the subscriber's profile or in a data extension field. If it is set to true, Marketing Cloud will not record any opens or clicks performed by that subscriber.

Tracking Extracts are a type of data extract activity that allows marketers to export tracking data from Marketing Cloud to an external system, such as a dashboard or a data warehouse. Tracking Extracts can be configured to include various types of tracking data, such as email sends, opens, clicks, bounces, unsubscribes, etc. Tracking Extracts can be combined with a File Transfer activity and an Automation Studio workflow to transfer the extracted file to the desired location on a daily basis.