Email marketing includes several different types of subscriber lists and suppression lists is one of them. A suppression list consists of all the email addresses that you don’t want to send emails to.
There are various automation rules that can be set up for suppression lists. Most marketers automatically send hard bounced emails to a suppressed list. The same goes for people who mark you as spam or simply unsubscribe.
Suppression lists are created to ensure a continued reputation for the brand by eliminating email addresses that don’t want to receive emails in the first place.
Most email marketing solutions offer only one suppression list so as to prevent any confusion or duplication.