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Review notes:
  • this doc includes details about the suppression hierarchy we mapped out in the internal features docs here Does this need to be covered in the external docs?
Sending email to invalid email addresses or recipients who don’t want to receive your emails can damage your (and Helo’s) sending reputation. To prevent that, we use suppressions. A suppression tells Helo not to deliver mail to a particular address. Before every send, Helo checks each recipient against your suppression list and silently drops anyone who appears on it, protecting your sender reputation and keeping you compliant with recipients who have bounced, complained, or opted out. Suppressions are scoped to a Channel and a mail type (transactional or broadcast), so an address suppressed on one Channel does not affect others.

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How addresses get suppressed

Most suppressions are created automatically as Helo processes delivery events. Here’s why an email address might land on your suppression list:
A hard bounce suppresses the address for both transactional and broadcast mail, since a non-existent or rejecting mailbox can’t receive either. Learn more about bounce types. Complaints and unsubscribes apply only to the mail type the recipient received.
You can view your suppression lists for each Channel and mail type in the dashboard or use the Suppressions API endpoint to pull them programmatically. For each suppression, we provide you with the suppression reason as well as date the suppression was created.

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Reason priority

An address can only carry one suppression reason per Channel and mail type. Reasons have a priority order — bounce < manual < unsubscribe < complaint — and a higher-priority reason overwrites a lower one. For example, if a manually suppressed address later files a spam complaint, its reason is upgraded to complaint. A lower-priority event never downgrades an existing suppression.

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What happens with suppressed addresses at send time

When you send an email with Helo, we check every recipient against the suppression list before sending. Suppressed addresses are removed from the To, Cc, and Bcc fields, and the message is delivered to whoever remains. The dropped addresses are returned in the suppressions array on the send response:
If every recipient is suppressed, the message is rejected with errorCode: "recipients_suppressed".

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Adding addresses to the suppressions list

You can manually add email addresses to your suppression lists, for example to honor an opt-out request you collected outside of Helo. You can do so via the dashboard or via the Suppressions API. Manually added addresses get the manual reason.

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Removing addresses from your suppressions list

If the underlying issue that caused the suppression has been solved, you can remove a suppression and start sending to that address again. You can remove suppressions with the reason manualor bounce via the dashboard or the API. Suppressions created by spam complaints or unsubscribes cannot be manually removed to protect deliverability. If you ever need to remove a suppression that falls into a category you can’t manage yourself, reach out to our support.