Never email someone who opted out

A home-decor retailer imports a fresh CSV of contacts from a trade show, not realising three addresses had unsubscribed from an earlier campaign months before under a slightly different list. The import quietly re-adds them, the next broadcast reaches all three, and one replies with a complaint that this business clearly does not respect an unsubscribe request — a complaint that damages the sending domain's reputation with every mailbox provider watching, not just that one recipient's opinion.

Suppression list management exists to make that scenario structurally impossible rather than something to remember. Every unsubscribe, hard bounce and spam complaint gets added automatically to a permanent do-not-send list, and every single outgoing send — a broadcast, an automation step, a CSV import, a CRM sync — is checked against that list before anything goes out. There is no manual override that lets someone re-add a suppressed address without a deliberate, logged re-opt-in step first.

The single most common way a suppressed address gets re-mailed is an import — a fresh CSV from a trade show, an event, a partner list — nobody checked against existing suppression before uploading. Suppression is not a manual step someone remembers to run; it is a preflight check baked into the pipeline, so every row in a new file is checked before it becomes mailable, the same way any send path is checked before dispatch.

The distinction between global suppression and marketing-only suppression matters more than it looks, and getting it wrong creates exposure either way. A hard bounce or spam complaint is scoped globally — no email of any kind should reach that address again, since it is likely invalid or the recipient has actively flagged the sender as unwanted. A marketing unsubscribe, by contrast, is scoped to marketing only, so a customer who opted out still receives their order receipt, a service communication owed to them, not a promotion declined. Confusing these two scopes either sends unwanted mail after an opt-out, or blocks a message a customer is entitled to.

Removal from suppression is deliberately made hard, by design rather than oversight. An address does not age off the list over time, and there is no bulk 'clean up the list' action that quietly restores addresses to mailable status — every removal needs a specific, logged re-opt-in reference showing the person actually asked to be added back. This exists because suppression that can be casually reversed undermines the point of honouring an unsubscribe or complaint permanently, protecting the retailer's domain reputation.