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Context

 

In Office 365 environments integrated with Proofpoint Essentials, a meeting invite originally received from an external sender may be forwarded internally. When this happens, Microsoft 365 can still interpret the message as external because it retains the header x‑ms‑exchange‑meetingforward-message. As a result, the message may be redirected again to Proofpoint, causing it to be filtered unnecessarily. To prevent this re-ingestion loop, an exception must be added to the Inbound Redirect Rule (US) in Exchange Online so that forwarded meeting‑related emails are excluded from the Proofpoint redirection.
 
You may experience the following symptoms:
 
  • Internal recipients do not receive forwarded meeting invites
  • The sender does not receive a bounce back message
  • Recipients are not added to the meeting event

 

You can confirm if your are impacted by this issue by checking the Proofpoint logs:

  1. Login to your Proofpoint Essentials console.
  2. Go to Email Logs.
  3. Search for:
    • The missing meeting invite subject
    • The internal recipient
    • Or the sender who attempted the forward
  4. If the invite is in Quarantine, this confirms the issue.

Solution

Add an exception to the Inbound Redirect Rule (US) in Exchange Online to prevent forwarded meeting messages from being redirected back to Proofpoint.

Steps to Add the Exception

  1. Open the Inbound Redirect Rule (US) in Exchange admin center.

     

  2. Click Add another exception.
  3. Choose Message header.
  4. Select Matches these text patterns.

  5. In Enter text, paste:

    x-ms-exchange-meetingforward-message

  6. In These text patterns, enter:

    Forward

     

  7. Click Save on the rule to apply your changes.

 

 

Keywords: Proofpoint Essentials, Office 365 integrated deployment, Email forwarding issue, Internal email filtered, Email re-ingestion,Forwarded email loop, x-ms-exchange-meetingforward-message, Inbound redirect rule, Exchange Online rule exception