Exchange 2003 Configuration
Versions 2013 and earlier of exchange have reached the official End-of-Life (EOL) with Microsoft and Microsoft has ceased support for these products. The following instructions were correct at time of writing, however, as these versions are no longer officially supported, we cannot guarantee the success of configuration.
Microsoft Exchange 2003 uses the Allow lists based on reverse DNS, therefore you can simply add *.hostname.tld to the Domain field. You can find this when following the instructions How to Configure IP Address Restrictions.
For Hosted Cloud users please use *.antispamcloud.com instead of your servers root hostname.
For local cloud users use your servers hostnames