Because the customer already possesses a fixed, curated list of known competitor email addresses — a static, externally-sourced list rather than a set dynamically derived from an internal query against existing behavioral or attribute data — the correct approach is to load these known addresses directly into an auto-suppression list, which then automatically applies to all qualifying future sends and prevents any of the listed addresses from receiving marketing communications going forward without requiring the list to be manually re-attached to each individual send. Populating it directly with the known email addresses (rather than subscriber keys, as in option B) is appropriate here specifically because the source data the customer has in hand is a list of raw email addresses, not internal subscriber key values, and the suppression mechanism can match directly against the email address field. Option A describes building a list via query to ' exclude the subscriber key, ' which misapplies a query-based approach to what is fundamentally a static, externally-provided list rather than data that needs to be dynamically derived through SQL logic. Option D ' s ' exclusion list ' is not the correct, standard Marketing Cloud terminology or mechanism for this scenario — auto-suppression list is the actual, documented feature that automatically applies across future sends. Reference: Auto-Suppression Lists.