The core of the proposed change is to use cloud storage exclusively for non-sensitive data. The success of this initiative hinges entirely on the ability of employees to correctly distinguish between sensitive and non-sensitive information. Therefore, the most critical and foundational element to include in the data management policy before implementation is a mandate for training employees on how to classify data. This ensures that the workforce understands their responsibility and has the knowledge to comply with the policy, thereby preventing the accidental upload of sensitive data to an unapproved environment. This is a proactive governance control that addresses the primary risk associated with the new process.

B. A mandate for the encryption of all corporate data files at rest that contain sensitive data This is incorrect because the policy change specifically addresses the storage of non-sensitive data; a control for sensitive data is not directly relevant to this initiative.
C. A process for blocking access to cloud-based apps if inappropriate content is discovered This is a reactive, technical enforcement measure. The foundational policy must first define what is appropriate, which is established through data classification.
D. A requirement to scan approved cloud-based apps for inappropriate content This is a detective control. The primary policy objective is to prevent inappropriate data from being uploaded in the first place, which is achieved through proper classification and user awareness.

1. ISACA, CGEIT Review Manual, 8th Edition. Domain 2: IT Resources, Section 2.4 Information/Data. The manual emphasizes that a data classification scheme is a fundamental component of data governance. It states that policies must define classification levels and handling requirements, and that personnel must be trained on these policies to ensure they are applied correctly. This establishes training on classification as a prerequisite for effective data management.

2. ISACA, COBIT 2019 Framework: Governance and Management Objectives. Management Objective APO14, Managed Data. Practice APO14.02, "Define and maintain a data dictionary and data governance policies and procedures," explicitly calls for establishing and communicating a data classification scheme. This underpins the need for a formal policy and user understanding before data is managed under new rules (e.g., moved to the cloud).

3. ISACA, COBIT 2019 Framework: Governance and Management Objectives. Management Objective APO07, Managed Human Resources. Practice APO07.03, "Maintain the skills and competencies of personnel," highlights the need to provide personnel with training to develop the competencies required to fulfill their roles, which in this scenario includes correctly classifying data according to policy.