You will need an account such that all the spam that arrives goes into the inbox. This means that you should disable content-based filtering at the mail server for this account. For example, in DeskNow you would log in to the account and go to preferences/mail/spam to control this. Whatever controls are available to the mail administrator to restrict the account should be put in place. Ideally you want an account that can receive e-mail, and do nothing else.
If you have multiple addresses that are the target of Spam, you can make them aliases of the account. The Spam Trap does not delete mail that has been read. This gives you the opportunity to dispose of it as you desire. Most people will log into the account once a week, and delete the older messages in order to keep the mailbox from getting full.
You will need to have your mail server machine use your DNS for all lookups. It wouldn't hurt to have all your machines using your DNS, so you should consider changing the settings in your router or DHCP server to put your server ahead of any external servers you use. This is required on the mail server machine.
You need to add
dnsrbl.mydomain.com to the list of blacklists used by your