zonecheck.org, formerly alt.backspace.org, was originally an in-house private DNSBL which was kicked off in 2003 originally whilst at our employer at the time, an Internet Service Provider, because it was time consuming replicating access lists across a bunch of SMTP servers, it was so useful it was kept maintained AFAIK by network staff even after change of employment in mid 2006, where I also recreated it as dnsbl.uni, the two lists remained separate which resulted in more freedom to do what I wanted with it to keep protecting my own, and friends servers.
Over time it expanded by granting access to some other smaller ISP's and Educational Institutions, this was originally by a distributed private zone, in around 2010 it got to a point that it was decided to open it to the public, as it was also adopted for use by a number of SMB's in Australia and New Zealand, this soon expanded to ISP's and Educational in Indonesia, U.K., Germany, France, Kuwait, Japan, and even the U.S.A. and Brazil towards, 2013/14, a well known search provider uses one of our lists in their scoring system.
Because we know those who submit entries to our spam/URI lists, it's considered to run with none to little false positives, we do not accept listings from anyone we don't know, only select ISP's in Australia, New Zealand, and Europe are in our submission trust group.
Our listing criteria is simple, send any of us spam, send to one of our many spam-trap addresses over many domains, or act in any grossly socially unacceptable way, you'll quickly end up listed, we don't care if you're Telstra BigPond, Verizon, SBCGlobal, BT, OVH, or some freemail service like Gmail or Yahoo - violate our listing policy, you WILL be listed, there are NO EXCEPTIONS!
If you have been directed here by a reject DSN message, then you need to stop spamming, or, are virus infected, acting as part of a botnet, or, have behaved in a miscreant manor, in which case you need to clean up your act and be a good netizen.
It may also be possible the blocking relates to a previous user of your IP address, if you feel your listing is unjust or in error, you can plead your case and have your ISP request a de-listing, but before doing so, ensure your network is clean of malware and viruses, and consider blocking outbound port 25 and use the mail submission port (587) for all users outgoing mail.
If you are the listed whois contact for your IP or range that's listed on bl.zonecheck.org and have resolved the cause, you may request delisting