What is Suppression list?
A suppression list is the set of addresses, domains or numbers you must never contact again, checked before every send regardless of which list a contact came from.
Also called: do-not-contact list, unsubscribe list.
It holds opt-outs, hard bounces, spam complaints, people who asked by reply not to be contacted, and anyone you have decided not to approach (existing customers, competitors, partners). The point is that it sits above every campaign and every tool: a contact who opted out of one sequence must not reappear in the next because a new list was imported.
CAN-SPAM requires opt-outs to be honoured within 10 business days, and once someone opts out you may not sell or transfer their address. A shared suppression list is how a team with several sending tools actually meets that. For phones, the same role is played by an internal do-not-call list alongside the Do Not Call Registry.
Suppress by domain as well as address when a business asks you to stop: a different employee's address at the same company is the same request in spirit.
67Leads keeps its own suppression list for businesses that opt out of the warehouse: an opted-out phone, domain or email is removed from every count, page and export, and stays removed when a later scan sees it again. Businesses can opt out at /remove.