Which of the following is NOT a valid way to populate Directory Groups?

The correct choice highlights that using Mimecast Archive is not a valid way to populate Directory Groups. Mimecast Archive primarily serves to store and manage email records for compliance, e-discovery, and retention purposes. It focuses on the secure archiving of emails rather than the dynamic management or population of user groups within an organization's directory.

In contrast, the other options are directly related to the integration and management of user directory groups. Mimecast for Outlook facilitates user interactions with their email, allowing connection to Mimecast's services, while Directory Connector is specifically designed to synchronize local directories with Mimecast's cloud services, ensuring that any changes in the local directory are reflected in the Mimecast environment. Additionally, the Mimecast Server Connection is utilized for integrating server-based mail systems with Mimecast, further supporting the population and management of directory groups. Each of these options is built to enhance the interaction and synchronization between user groups and the Mimecast platform.