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Signal cannot guarantee that a recipient mailbox places a message in the inbox. It can provide specific evidence before, during, and after delivery.

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Evidence Signal can provide

None of those signals proves inbox placement or human reading. A recipient server can accept mail and place it outside the inbox.

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Product controls you can verify

  • The From domain remains verified.
  • DKIM, MAIL FROM, SPF, and relevant DMARC state are healthy.
  • The recipient is not globally unsubscribed or suppressed.
  • Topic sends resolve opt-in subscribers.
  • Bounce, complaint, unsubscribe, suppression, rejection, and failure trends are visible in metrics and events.
  • Tracking uses the intended project domain and settings.

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When delivery health changes

  1. Choose a fixed comparison window.
  2. Separate sent from delivered.
  3. Compare bounce, complaint, rejection, failure, and suppression counts.
  4. Check the sending domain’s component statuses.
  5. Review recent DNS, From-address, audience, content, and volume changes in your own change history.
  6. Inspect DMARC sources for authentication changes.
  7. Pause automated retries to recipients with terminal feedback.

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Engagement caution

Open and click events are directional. Image blocking can hide opens, privacy systems can load images, and security scanners can follow links. Use application conversion or customer action as separate evidence when that distinction matters.
Do not report delivered as “in the inbox.” The verified statement is that the recipient mail server accepted the message.