Rules for user alias to reject External emails

Question

Hello,

Scenario: Senior members of our staff receive unsolicited emails. Commonly external people guess the email address, so they are not spam, but should be directed to our public facing inboxes.

The challenge I have is to prevent these messages from being received. One option I looked into was mail rules, using the Header 'To:', and Block/Reject Reject the email with a message. However the rejection message is the lengthy Office365 rejection message with tips and reasons the message could not be delivered, which is not what I want. is there a way to reject a message with a simple "This mailbox is not monitored" type response? without looking at Auto-replies.

I looked at Auto-replies, but that then blocks legitimate incoming external emails for the staff members. Ultimately we could just create a new mailbox for the staff member, but that seems to be more trouble than its worth. Wondering if anyone has any elegant solutions to a similar problem.

Thanks

Answer 1

Hi @Stephen Potts,

Thank you for posting to Microsoft Community.

Based on your description, I understand you want to reject the email with customer message in mail flow rule.

However, I am afraid you can only include the reason with O365 Non-Delivery Report(NDR) message as the screenshot below.

You could refer to Mail flow rule actions in Exchange Server | Microsoft Learn for more information.

If my answer is helpful to you, please mark it as the answer so that other users can refer to it. Thank you for your support and understanding.