There are several spam detection and blacklist services that identify email and IP addresses that send unsolicited email messages. As a general rule, don’t send any mailings to these organizations. It will only increase the potential of ending up on one of the lists which they manage.
CheckMarket assists you with this by automatically blocking the import of known addresses and domains.
The * can be replaced by any character, e.g. both the domains @goingto.test.com and @12345.test.com – and consequently any variations thereof – will be blocked.