Can't forward messages externally

Question

I am trying to forward any emails sent to externally. When doing so we get error. Don't allow forwarding by default in our antispam policies but want to make an allowance for this one mailbox.

I created the following anti-spam policy but it doesn't seem to work. Please can you advise?

Answer 1

Hello Yatif,
   Good day! Thank you for posting in the community.

Based on your description, it seems that your organization has a default policy that blocks external forwarding for security reasons. To allow an exception for a specific mailbox, you would need to adjust both your anti-spam and outbound mail flow rules. Here are the steps to configure the exception:

Adjust Anti-Spam Policy for External Forwarding:

Since the current anti-spam policy blocks external forwarding, you need to modify it:

• Navigate to the Microsoft 365 Defender portal:
  1. Go to https://security.microsoft.com/
  2. Under Policies & rules, select Threat policies.
  3. Select Anti-spam policies.
• Create an Exception for a Specific Mailbox:
  1. In the anti-spam policy, select the existing policy blocking forwarding, or create a new one.
  2. Under Outbound spam filter policy, check if forwarding is disabled.
  3. To make an exception for the mailbox, go to the Policy exclusions section.
  4. Under Recipient filtering, add the specific mailbox for which you want to allow forwarding.

Configure Outbound Mail Flow Rules (Transport Rules)

If the anti-spam change alone does not work, try configuring an outbound mail flow rule in Exchange to allow forwarding for the mailbox:

1. Open the Exchange Admin Center:
   • Go to https://admin.exchange.microsoft.com/.
2. Create a New Mail Flow Rule:
   • Go to Mail Flow > Rules.
   • Select New Rule > Create a new rule.
3. Set Conditions:
   • Name the rule (e.g., “Allow External Forwarding for [Mailbox Name]”).
   • Under Apply this rule if..., select The sender is and choose the mailbox in question.
4. Action:
   • Choose Modify the message properties > Set the message header.
   • Add the header value:
     • Header name: X-MS-Exchange-Organization-BypassClutter
     • Value: true
   • This should allow external forwarding for the specified mailbox.
5. Save the Rule.

Verify the Changes

• Once both the anti-spam and outbound rules are in place, test forwarding again from the mailbox to an external recipient.

If you’ve checked all these settings and are still having this situation, you might also take advantage of having Office 365 Business subscription as it will give you real-time and advanced technical assistance to solve this matter. This process typically involves the Office 365 Global Admin conducting a remote session to gather advanced logs. If necessary, a technical support engineer can escalate the issue to a specialized team for further investigation.

As forum members we don’t have the capability to collect or analyze these logs due to privacy and access constraints, the best course of action is to engage Microsoft support directly.
 
You can refer to this article for guidance on creating a service request from the Office 365 Admin Center to receive further assistance: Get support - Microsoft 365 admin | Microsoft Learn. 
 
For creating a support request, you might need to contact the IT admin of your organization: How do I find my Microsoft 365 admin? - Microsoft Support. 
 
Note: If you’re an end-user, please coordinate with your Office 365 Global Administrator to handle these steps.   

Appreciate your patience and understanding. Have a great day!