Exchange rule issue with "Prepend the subject of the message with"

Copper Contributor

Dear all,

I am encountering an issue that I have been unable to resolve despite researching extensively online.

Contextually, I need to forward all incoming emails from a distribution list to a shared mailbox. To identify these forwarded emails in the shared mailbox, I attempted to add a text to the subject line (namely, "The DL should no longer be used by my colleagues in a few months").

Here's what I've done so far:

  • Condition: "Recipient", "Address matches any of these patterns" (I've also tried "The sender address includes")
  • Actions:
    • "Add the recipient:" "to the Cc Box" => my shared mailbox
    • "Prepend the subject of the message with"

The forwarding is working as expected, but the subject line is not being prepended with the chosen text.

Have I missed something?

Thank you all in advance for your help.

Best regards, Guillaume

10 Replies

@Guillaume365 Have you tried to swap the two actions: first prepend the text, than CC the mail?

@Deleted Thanks for you prompted reply. Yes I also tested to invert the 2 actions, and I get the same behavior.

@Guillaume365 What about the original recipient: does he get a modified subject line?

Both received the same email with same subject. :\
Could you please post the output of Get-TransportRule for this rule (with anonymized data where necessary)?
1) Try to add X-header instead of prepending the Subject
2) To identify these forwarded emails in the shared mailbox you can create a Power Automate flow.

Dear @Deleted,

I apologize for the delayed response. Upon investigation, it was discovered that the Distribution List had already been triggered by an Outlook Web App Rule. Even after removing the rule, my exchange rule still wasn't functioning. Neither of my actions were working.

However, I noticed that if I replace the Distribution List with a Microsoft 365 List (originally "email address removed for privacy reasons," but with a new alias "" set as default), the same exchange rule works well.

Could this be a compliance issue?

Best regards,


I am not familiar with Office 365, I work "on premise". I'm sorry I can't help you here.

@Deleted i finaly find the solution, this may help other people who are stuck like me.

The only one fact that my rule was not working was that we can't use the condition "the recipient is" if recipient is a Distribution List, you must use the condition "includes any of these recipients in the To or Cc box:"


I hope this will help.



Thank you! Had exactly the same problem. This worked perfect!!