Deliverability & the inbox
Suppression list
Also known as: do-not-send list · bounce list
The list of email addresses that must never be sent to — unsubscribes, hard bounces, spam complaints, and known-invalid addresses. Required by law in most jurisdictions; required by deliverability discipline everywhere else.
A suppression list is the set of email addresses an ESP is prohibited from sending to, regardless of what the brand's marketing database says. Categories: unsubscribes (user opted out), hard bounces (the address doesn't exist or the mailbox is full), spam complaints (user hit "mark as spam" in their inbox), role accounts (info@, support@ — often policy-suppressed), and manually-added (customer service requests, legal holds). Suppression lists are required by CAN-SPAM (10-day unsubscribe processing) and GDPR (honour withdrawal of consent). Beyond law, maintaining a clean suppression list is how you protect sender reputation — sending to a hard-bounced address repeatedly is a strong spam signal to mailbox providers. Most ESPs manage suppression automatically, but operators should audit quarterly: old addresses that haven't engaged in 12+ months should be proactively suppressed even before a bounce.
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