Definition
A suppression list prevents future delivery to contacts who unsubscribed, complained, hard bounced, or were blocked for another policy reason. It is an operational safety control, not merely a list segment.
Suppression can apply globally, to marketing only, to one list, or to a specific message type. Scope matters: a marketing unsubscribe should stop promotional mail without necessarily blocking a requested password reset.
Why it matters
Suppressions protect recipient choice, legal compliance, cost, and sender reputation. They must survive imports, integrations, list replacement, and migration to a new sending platform.
How it works
- 01
An event such as unsubscribe, complaint, or hard bounce creates a suppression record.
- 02
The record stores reason, scope, source, and timestamp.
- 03
Every send checks applicable suppressions before enqueueing delivery.
- 04
Authorized resubscription follows a documented process without erasing historical evidence.
Example
[email protected]
reason: user_unsubscribed
scope: marketing
source: footer_link
created_at: 2026-07-27T14:05:00Z
Marketing campaign: blocked
Requested password reset: allowedCommon mistakes
- Deleting unsubscribed contacts and losing the do-not-send record.
- Re-importing an old list over current suppressions.
- Applying a marketing unsubscribe to critical requested transactional mail without defining scope.
- Allowing ordinary campaign users to remove complaint suppressions casually.
Key takeaways
- Store reason, scope, source, and time.
- Check suppressions at the final send boundary.
- Carry suppression data through every migration.