How To Allow Relay Exception In Exchange 2007 Receive Connector

There are situations in which you need to allow emails to relay through your exchange 2007. For example, in my case, our clients have their own system which generate newsletters and send it via emails. They don’t authenticate with our SMTP server, all they need is our SMTP server address in order to route the message. Hence we will need to setup a custom receive connector to allow relaying from an unauthenticated systems.
In order to allow our exchange to be able to relay from third party systems, follow these step by step guides.

Start Exchange Management Console.
Browse to Microsoft Exchange -> Server Configuration -> Hub Transport.
Select “New Receive Connector…” on the Actions pane.
In the New SMTP Receive Connector wizard, type in a name for the connector. Then select the intended use for this receive connector options. For our case select “Custom”. Click next.
Select the default local IP address and click on the Edit button, then type in your server’s local network IP address and leave the port at 25. Click OK and Next to continue.
In the Remote Network settings page, select the default value and click on the X icon to delete it. Then click the Add button to type in your remote IP address. Let’s put that my third party newsletter server IP address is 202.188.166.78. Click Next.
In the summary page, you will see your new SMTP Receive Connector’s Name, Type, IP address and Remote IP address. Once confirm the information is correct, click New to create it.
You will see your newly created receive connector appear on the Hub Transport page. Right click on it and select Properties.
Switch to Permission Group tab, and select the Exchange servers checkbox. ( Note you must do this to continue.)
Next switch to the Authentication tab, select the “Externally Secured (for example, with IPsec)” checkbox.
Click Apply and OK button.