A suppression list is a list of email addresses (and sometimes whole domains) that must never be emailed. Every campaign checks it before sending, whichever mailbox the email would come from.
Who goes on it
- Anyone who unsubscribed or asked to be removed, by link or by reply.
- Addresses that hard-bounced.
- Your existing customers and current deals, so sales outreach doesn't reach them by mistake.
- Competitors and partners, often by whole domain.
Why it matters
Emailing someone who opted out breaks the CAN-SPAM Act, GDPR and most other rules, and gets you spam complaints. With many mailboxes and campaigns, only a shared list guarantees a "no" in one place is respected everywhere.
Keeping one
Add to it automatically from unsubscribes, "remove me" replies and bounces; never delete from it. Build or tidy one from your unsubscribes, bounces and customers with the free suppression list builder.