Different Types of IP Blacklists
First, there’s internal blacklists and third-party blacklists. Many small and media-sized mailbox providers use third-party blacklists (Spamhaus, Barracuda, etc) because they don’t have the resource or time to build their own. Big mailbox providers like Gmail, Outlook, and GMX use their own internal blacklists. Actually, GMX uses both internal and third-party blacklists. Then, there’s single IP blacklists and whole IP range blacklists. It’s often very easy to request IP removal from single IP blacklists. It’s not that easy to get off a whole IP range blacklist. Luckily they are not commonly used.