The elements which are given in the black list are always denied access. This is opposite to the white list which contains the list of items that are granted access through any gate that is used. Generally, the black list contains the list of IP address or the email names from the known or potential spammers. It is a common feature in most of the Anti-Virus tools.  Black list option is often used by both the enterprises and individuals to screen unwanted emails and potential spam.