No bounced back notice after sending to an invalid email address

Hi @Viola Lau

Thank you for posting your question in the Q&A Forum.

It can be quite tricky managing NDRs in a shared environment because, by default, Exchange tends to route these notifications to the individual sender's primary mailbox rather than the shared one. This often makes it seem like the NDR has vanished.

If you are looking to configure the shared mailbox so that it receives its own bounce-back notices, here is some guidance you can share with your IT team:

1. Suggested Configuration (PowerShell)

The most effective way to handle this is via Exchange Online PowerShell. There isn’t a direct toggle in the Outlook interface, but your admin can run this command to ensure a copy of "Sent As" reports stays within the shared mailbox:

Set-Mailbox -Identity "******@yourdomain.com" -MessageCopyForSentAsEnabled $True

2. Immediate Check for the User

In the meantime, you might want to ask the user who sent the email to check their personal Inbox and Junk folders. Usually, the "Undeliverable" notice is sitting there because the system identifies them as the actual "originator" of the message.

3. Server-Side Verification

If the NDR is still missing, your IT admin might want to check the Remote Domain settings in the Exchange Admin Center to ensure that "Allow non-delivery reports" is enabled for external recipients.

For more detailed technical steps and official documentation, these resources might be very helpful:

• Messages sent from a shared mailbox aren't saved to the Sent Items folder - Exchange | Microsoft Le… - This covers the -MessageCopyForSentAsEnabled logic which applies to system reports as well.
• Remote domains in Exchange Online | Microsoft Learn - Guidance on ensuring NDRs are allowed to be sent/received across your organization.

I hope this helps you get the shared mailbox tracking correctly. Please let me know if you'd like me to look into anything else.

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