If you have chosen to use the BMS method of using MIPSpace, you have the advantage of knowing that it is independent of DNS lookups, and is not subject to problems performing remote lookups. However, you will need the BMS client to perform the lookups.
When you register for the BMS method, you will be given full instructions how to use this client with the mail server of your choice. This method allows you to integrate into almost any proprietary systems as well. There are specific BMS clients designed to work with some existing mail servers already, such as 'MagicMail' and 'Postfix', but the most simple form of BMS lookup is to use the 'bmslookup' tool that is also provided with your package:
bmslookup -c [path to your BMS Uncompressed Binary Data File] [ip Address]
This will return a simple 0 or 1 depending on whether it is listed.
For more information, please see the documentation that accompanies your registration.