Information
This parameter is used to decide if messages whose recipient doesn't exist in the organization are blocked. When this parameter is set to $true, the Recipient Filter Agent blocks these messages.
Note: The Set-RecipientFilterConfig cmdlet must be enabled
Rationale:
Spam originators may use a technique that involves first creating fabricated names, and then monitors for rejected emails due to non-existent recipients. Emails with names who are not rejected are then used for future spam mailings. To deprive the spam originator of valuable information, it is recommended to receive all messages, then evaluate and dispose of them as deemed necessary.
Impact:
Some legitimate messages might be blocked.
Solution
To implement the recommended state, execute the following PowerShell cmdlet:
Set-RecipientFilterConfig -RecipientValidationEnabled $true
Default Value:
False