The suppression list is the safety net that stops you emailing someone who should never hear from you again.
How addresses get on it:
- Unsubscribed, when someone uses the global unsubscribe link
- Bounced, when a hard bounce proves the address does not exist
- Complained, when someone marks your email as spam
- Manual, when you add an address yourself
What suppression does:
A suppressed address is excluded from every send, no matter which list, segment or audience it appears in. The check happens at send time, so it cannot be bypassed by clever audience rules. Imports also skip suppressed addresses rather than resurrecting them.
Why hard bounces matter:
A hard bounce means the mailbox does not exist. Continuing to mail dead addresses is one of the fastest ways to damage your sender reputation, because mailbox providers read it as a signal that you do not maintain your list. Automatic suppression on hard bounce protects you from that.
Complaints are the serious one:
A spam complaint is the strongest possible negative signal. If your provider supports complaint feedback, those addresses are suppressed immediately and permanently. Never re-add someone who complained.
Unsubscribes are per list or global:
The one click unsubscribe link in a broadcast removes that person from the list the email was sent to. The global unsubscribe stops everything and adds them to suppression.
Viewing the totals:
The Deliverability tab shows the counts by reason. Rising bounce numbers after an import usually mean the imported list was old or poorly maintained.