What is a suppression list?

Suppression list is the universal "do not send" list maintained by every reputable ESP. An address on the suppression list is permanently blocked from receiving any campaign sent through that ESP, regardless of which audience, segment, or list contains it.

Addresses land on the suppression list:

• Automatically. After a hard bounce, after the user clicks unsubscribe, or after a spam complaint reaches the ESP via feedback loops.
• Manually. When you add specific addresses (employees, journalists, known abusers).
• Via API. When you suppress addresses programmatically before they ever receive a campaign.

The suppression list is one of the most important compliance and deliverability mechanisms in modern email. Without it, unsubscribed users would receive future campaigns (a regulatory problem under CAN-SPAM, CASL, GDPR), and hard-bounced addresses would continue to accumulate bounces (a deliverability problem).

See what is a suppression list for the full practical guide.