List hygiene

List hygiene is the recurring chore of getting addresses off your list that no longer belong there: hard bounces, addresses that keep failing temporarily for weeks, and subscribers who have not clicked, replied, or shown up in six to twelve months. Mailbox providers grade you on how your recipients behave, so a list padded with dead addresses drags down every message you send, including the ones real people wanted.

Two categories deserve a lighter touch than deletion. Role accounts (info@, sales@, support@) are not invalid, and plenty of them are legitimate opted-in subscribers at small companies, so flag and review rather than purge. Suspicious typos (gmial.com, hotmial.com) should be caught at the form and confirmed by the person typing them. Silently rewriting a domain is how you deliver somebody's receipts to a stranger who happens to own the misspelling.

Do it on a schedule, not in a panic. Bounces get removed automatically the day they happen through provider webhooks. Inactives get a re-engagement campaign ('still want these?'), then a sunset policy that quietly stops mailing anyone who ignores it. Before a first send to a list older than a few months, a validation service will strip the syntactically broken and clearly unroutable addresses, which is worth doing, but it cannot prove an address is safe and it cannot reliably spot a spam trap. Treat its output as triage, not absolution.

The gotcha most people meet the hard way: an old list is not neutral, it is actively dangerous. Abandoned addresses get recycled by providers into spam traps, and one hit can get your domain listed. The other trap runs the opposite direction. Apple Mail Privacy Protection opens almost everything on the recipient's behalf, so 'opened' is now a weak signal. Judge inactivity on clicks, replies, and site visits rather than opens, or you will keep mailing corpses and cut off real readers.