The built-in email system is designed for emailing active members of your site whom have requested to receive emails from you. A good example of a good use for this too would be to send a monthly newsletter to your members. The email system will also send transactional emails that include new member signup notifactions, credit card update notifications, and lead emails.
Sending mass unsolicited emails to the Claim Listings or an imported contact list would be considered SPAM, which is illegal by US law and would likely result in the blacklisting of future emails from your domain. In some cases, sending SPAM messages may lead to damaging the other sites on the server and can also lead to the termination of your account with Brilliant Directories.