How do I reject incoming email for unknown users in MS Exchange 2007, 2010, 2013, 2016?
This solution is for Exchange Servers 2007 and later and using the anti-spam agent for exchange. This is an available feature in the Edge Transport Server. However if you don't have Edge Transport Server it is possible to install the anti-spam agent in the Hub Transport Server. Instructions for this can be found here.
- Start the Exchange Management Shell (EMS)
- Type the following:
Set-RecipientFilterConfig -RecipientValidationEnabled $True
This solution will be prevent backscatter and stop your exchange server generating masses of NDR's (Non-delivery reports) for unknown users.