Scenario - User creates Outlook rule to forward all email to an external address. For whatever reason, that external mailbox starts rejecting the incoming messages and sends an NDR, which is received by the internal mailbox and then forwarded back out, thus creating a loop on the mail server.

As the Exchange administrator, how can I be notified when this is occurring so that I can disable their mailbox? We recently had an instance that dumped 500K messages in one mailbox.

Thanks!

Hi.

Create a rule lock (or with moderate)  automatic transmission.

Example.

How to prevent internal users from autoforwaring mails to external recipients

or used PowerShell

Get-InboxRule

Example: Get-InboxRule -Mailbox User_mailbox | Select Name, Description | f

No, I lost the battle to prevent auto-forwarding long ago.  Now I just need to know when the loop is occurring so that I can disable the user's mailbox and stop the loop.

Hi,

For your question, we need foud out whose mailbox cause this issue.
Please run below command to list inbox rule:

foreach ($i in (Get-Mailbox -ResultSize unlimited)) { Get-InboxRule -Mailbox $i.DistinguishedName | where {$_.RedirectTo -or $_.ForwardTo -and -not ($_.description -match "If the message")} | fl MailboxOwnerId,Description >> rules.txt }

Then you can try to modify relevant inbox rule or disable it.

Thanks

There are about 100 users with forwarding rules.  What I am trying to accomplish is to create an alert whenever ANY mailbox has a forwarding loop.

Hello

You need to analyze the loop email header for the value "X-Loop" if it has some values. You can create a transport Rule with this value if any detected.

and you can created another rule using this value to delete that loop and inform you.