A whitelist is a list or register of entities that are being provided a particular privilege, service, mobility, access or recognition. Entities on the list will be accepted, approved and/or recognized. Whitelisting is the reverse of blacklisting, the practice of identifying entities that are denied, unrecognized, or ostracized. Whitelists are commonly applied to email addresses and IP addresses. In the case of email address whitelists, emails not in the whitelist are ignored or flagged as spam. In the case of IP address whitelists, IP's not in the whitelist are unable to gain access to the server.