Prior to decommissioning an IT system, it is MOST important to:

Assessing compliance with environmental regulations is important for physical disposal, but secondary to ensuring data retention requirements are met.

Assessing compliance with the retention policy ensures that all data residing on the system has met its required retention period or has been properly archived or migrated before the system is retired and its data is potentially destroyed. This prevents premature disposal of legally or operationally critical data and avoids non-compliance issues.

Reviewing media disposal records occurs *after* data has been disposed of, not prior to decommissioning when retention is the primary concern.

Reviewing data sanitation records is a check performed *after* data has been sanitized, which is a step that follows the determination that the data can indeed be disposed of according to retention policies.