List hygiene

List hygiene is the routine of removing addresses that no longer belong on a mailing list: hard bounces, role accounts, typo domains and contacts who have not engaged for a long period. It protects the reputation everything else depends on, since recycled spam traps live almost entirely among old, unengaged records. Validation services catch syntax errors and dead mailboxes, but they cannot tell you whether a real person still wants the mail. Engagement history answers that.