Restart-Service MSExchangeTransport

To enable the feature, run:

      Enable-TransportAgent "Recipient Filter Agent"

To verify that the accepted domains use the AddressBook to verify existing recipients. It is normally the default when an Exchange has been defined as mail server authority for one domain. To verify that, just type the following command:

      Get-AcceptedDomain | Format-List Name, AddressBookEnable

And verify if the list of all domains appears. To enable for all domains (caution, make sure you are not relaying any domains before running this):

Get-AcceptedDomain | ? {$_.AddressBookEnabled -ne "True"} | Set-AcceptedDomain -AddressBookEnabled $true

Verify if the list of all domains appears. To enable for all domains (caution, make sure you are not relaying any domains before running this):

      Get-AcceptedDomain | ? {$_.AddressBookEnabled -ne "True"} | Set-AcceptedDomain -AddressBookEnabled $true
      Restart-Service MSExchangeTransport

Enable validation with the following command:

      Set-RecipientFilterConfig –RecipientValidationEnabled $true

It is important to deactivate the filtering for the incoming mails on the Exchange if not already done! To verify what is activated:

      Get-ContentFilterConfig | Format-List

Now with the following command, the filtering for the incoming email can be deactivated:

      Set-ContentFilterConfig -ExternalMailEnabled $false

Disable now all other unnecessary (and bad) filter - accepty with (Y)es if needed:

      Set-SenderFilterConfig -Enabled $false
      Disable-TransportAgent "Sender Filter Agent"
      Set-SenderIDConfig -Enabled $false
      Disable-TransportAgent "Sender ID Agent"
      Set-ContentFilterConfig -Enabled $false
      Disable-TransportAgent "Content Filter Agent"
      Set-SenderReputationConfig -Enabled $false
      Disable-TransportAgent "Protocol Analysis Agent"
      Restart-Service MSExchangeTransport

Verify again:

      Get-TransportAgent

Now configure the Hub Transport receive connector to receive filtered email, and correctly validate users addresses issue the command:

      Get-ReceiveConnector | fl name,bindings

Note the name of the connector with binding ending :2525 (listening on connections from port 2525).
Set the receive connector to accept unauthenticated SMTP connections using command:

      Set-ReceiveConnector -identity 'connector name from above' -PermissionGroups 'AnonymousUsers, ExchangeUsers, ExchangeServers, ExchangeLegacyServers' 

      Restart-Service MSExchangeTransport