How does a suppression list work?
Before a message leaves the platform, every recipient is checked against the suppression list. Addresses land on it three ways: the person unsubscribed, the address returned a hard bounce, or the recipient marked the message as spam. A match means the send is skipped — no exception for segments, campaigns, or journeys that happen to include the address. Good platforms also record why and when each address was suppressed, so the exclusion survives CSV re-imports and CRM syncs.
Why is suppressing a contact different from deleting one?
Deleting a contact erases the very record that says 'do not message this person'. If the same address comes back through an import or a signup form, the platform treats it as new and mails it — exactly what the person objected to. Suppression keeps a minimal do-not-contact record instead. Under GDPR this is the accepted way to honor an objection to direct marketing: you retain the address for the sole purpose of never contacting it, alongside the consent record that documents the objection.
Why it matters for a two-person team
Mailbox providers score senders on complaint and bounce rates, and small senders have thin margins — a handful of complaints on a 2,000-address list moves your rate more than a thousand would at enterprise volume. A suppression list caps both rates automatically, with no manual review. It is the cheapest deliverability protection there is; for the wider picture, see email deliverability for startups.