There are two primary types of blacklists, local blacklist and third-party or distributed blacklists.
Local lists are maintained by a specific organization or site, and are generally updated manually when an administrator feels that a particular sending domain, person or IP address should be blocked.
Third-party, or distributed lists, are made publically available, and are set up for receiving-mail programs to dynamically query them. If your issue involves a third-party blacklist, be sure to note that there is a difference between the list owner/manager who operates the list, and the entity that is using the list. Even if a network is blacklisted on a third-party list, email from that network will only be blocked if the receiving entity is using that blacklist.