Inclusion in either of the MAILSPIKE Blacklists (BL or Z) means that your IP Address has most likely been identified as being part of a real-time spam outbreak. More specifically, Mailspike lists IPs that are part of a distributed spam wave and does not take into consideration over-time IP behavior. It is also worth noting that this RBL is a zero-hour list, meaning that you can be listed and then unlisted very quickly. Please remember that normal propagation will occur and while your IP address may be unlisted on the Mailspike site, other services which query their database could still show you as listed until the listing expires.
Mailspike Z Reports Subnets
Subnet-based Blacklists are used to reject email from entire ranges of IP Addresses, i.e. providers that are hosting companies sending spam, as well as single IP Addresses that may fall in that range of IP Address.