Your recipients may get this warning message on Outlook because of the Spoof Intelligence from Microsoft 365 Advanced Threat Protection and Exchange Online Protection. You can refer to this Microsoft article for more information.

To resolve this issue, follow the steps below:

  1. Login to Microsoft admin console.

  2. Go to Security & Compliance Center.

  3. Go to Threat management > Policy > Anti-spam.

  4. Under Anti-spam settings, expand the Spoof intelligence policy.

  5. Choose one of the following:
    • Review new senders
    • Show me senders I already reviewed

  6. If your campaign is trying to spoof your organization's domain, switch to Your domains. For campaigns that spoofs external domain, switch to External Domains.

  7. Select "Yes" under the Allowed to spoof? column for Phish Insight.
    Note: Phish Insight's sender address is