Glossary
Suppression list
List of addresses you must not send to — bouncers, unsubscribers, complainers.
A suppression list is the ESP's internal list of email addresses that further sends are blocked to. Each address lands there after one of these events:
- Hard bounce — address doesn't exist. - User complaint — recipient hit "Spam" in their mail client. - Unsubscribe — opt-out via List-Unsubscribe or preference center. - Soft bounce converted to hard after 5 retries.
Sendersy records all these events automatically. Subsequent POST /v1/emails calls to a suppressed address return an error.
This protects your IP reputation: if you kept hammering spammers and complainers, your domain would land on blocklists.