Mail rule exception for Send on Behalf messages

Question

Hello

I have a rule set up in Exchange > Mail Flow > Rules to add a disclaimer to all emails from members of a specific group. That is working.

As part of that rule, I have an exception to not add the disclaimer if a specific word appears in the subject line. That works as well.

However, I find that if a user has Send on Behalf rights from another mailbox, and she sends a message that way, the exception is ignored, and the disclaimer appears.

How can I get the exception to work for a Send on Behalf email, same as it does from the user's own mailbox?

Answer 1

Hi @Denis Repp, 

Welcome to the Microsoft Q&A forum. 

Thank you for outlining the scenario and the steps you already tried. Based on the details you shared, I understand you have a mail flow rule that adds a disclaimer for members of a specific group with a subject keyword exception, and that when a user sends a message with Send on Behalf in Outlook on the web the exception is not honored and the disclaimer is still added.  

This behavior occurs because, with Send on Behalf, Exchange can evaluate sender conditions against a different address than the visible From address. Consequently, if the rule checks the envelope sender rather than the header From, the exception may not be matched and the disclaimer action can still apply. When the rule is configured to evaluate the header sender, Send on Behalf messages are assessed consistently and the exception is applied as expected.  

To address this, please follow the steps below that suit for your situation: 

1/ Align the rule with the header sender 

• In Exchange admin center, open the rule and, under Set rule settings, change Match sender address in message to Header.  
• This ensures the rule evaluates the same visible From address used by Send on Behalf.  
• Reference: Set-TransportRule (ExchangePowerShell) | Microsoft Learn 

2/ Guarantee the keyword exception with a short pre rule 

• Create a new rule above the disclaimer rule that looks for your keyword using the Subject or body matches these text patterns condition and then sets a simple header such as XBypassDisclaimer with the value true.  
• Next, add an exception to the disclaimer rule that skips stamping when that header is present.  
• This pattern makes the exception reliable for both direct sends and Send on Behalf.  
• Reference: Mail flow rule conditions and exceptions (predicates) in Exchange Online | Microsoft Learn 

3/ Reorder and test from Outlook on the web 

• Place the new pre rule above the disclaimer rule, then send two quick tests using Send on Behalf, one with the keyword in the subject and one without.  
• Allow time for the rules to propagate as updates can take up to thirty minutes to become effective.  

4/ Contact IT administrator:  

Since your account is managed by your organization, please contact your IT administrator to review your permissions and policies. If the issue persists after these checks, ask your IT administrator to submit a support request directly to Microsoft Support team.       

They can raise a support ticket by visiting: Get support - Microsoft 365 admin | Microsoft Learn 

As community moderators, we appreciate your understanding that our access to internal development details is limited. Our primary role is to guide users toward the appropriate resources and support channels. While we may not have visibility into deeper backend analysis, we’ll continue doing our best to support you within the scope of our responsibilities.     

I hope this information is helpful. Please follow these steps and let me know if it works for you. If you have any updates regarding the issue, please feel free to share them with me.       

Thank you for your patience and your understanding. I look forward to continuing the conversation.  

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Answer 2

nice to see that AI still cannot understand a question, or give a useful explanation as to what to do to fix a problem

Answer 3

In Exchange, when a user sends an email using Send on Behalf rights, the message is treated as being sent from the mailbox of the user on whose behalf the email is sent, rather than from the sender's own mailbox. This can affect how mail flow rules and exceptions are applied.

To ensure that your exception for not adding the disclaimer works for emails sent on behalf of another user, you may need to adjust your rule to account for the original sender's mailbox. Unfortunately, the standard conditions and exceptions may not directly support this scenario, as they typically evaluate based on the mailbox from which the message is sent.

One potential workaround is to create a separate rule that specifically checks for the Send on Behalf condition and applies the same exception logic. This may involve using PowerShell commands to create more complex conditions that can evaluate the sender's original mailbox in conjunction with the subject line check.

You might also consider reviewing the priority of your rules to ensure that the exception rule is evaluated correctly in relation to the disclaimer rule.

For further details on configuring mail flow rules and exceptions, you can refer to the documentation on mail flow rules in Exchange Online or Exchange Server.