Suppression list

A suppression list is checked before every send, whatever the campaign or the list it came from. It usually holds four kinds of entries: people who unsubscribed or asked not to be contacted, addresses that hard-bounced, people who marked mail as spam, and companies you should not prospect, such as current customers, open deals and partners.

The list has to be shared across every tool that sends. If unsubscribes recorded in one tool are not known to another, the same person is emailed again, which breaks the law in many places and drives complaints. It also has to survive list imports. Suppressing whole domains, not only addresses, is how a customer's colleagues are kept out of cold campaigns. A suppression list is kept, not cleaned; entries leave it only when the person asks to hear from you again.