Define list categories and scope
Separate opt-outs, invalid addresses, and temporary delivery failures. A transient response may call for a delayed retry, while a clear unsubscribe or confirmed invalid mailbox should block future sends of the relevant message type.
Decide whether suppression covers one campaign, one category, or all nonessential mail. Preserve transactional messages only where the recipient relationship and applicable requirements permit them.
Keep updates reliable
Normalize addresses consistently and record source, time, reason, and scope while limiting access to personal data. Check suppression in every sending path so alternate jobs cannot bypass it.
Provide a controlled correction or consent update process. Review growth and reasons, then test that unsubscribe and bounce events take effect before the next send.