We view this particular blacklist as a very 'bad' blacklist and delisting is unfortunately not always possible. This blacklist checks on non generic reverse DNS for an entire /24 range (which we have not set for IP's in that range that are being assigned to a server, nor can we enforce customers to set them) and blocks that entire range after receiving spam from one or two IP addresses in the range.
Because we are not informed on what these specific 'offending' IP addresses are, we can't request delisting fot the entire range. We have no way of knowing which customer has to resolve these issues, so we can subsequently request delisting for the correct IP address.
Very recently Spamrats has added the possibility to request delisting for your IP if your range is listed, however this will only work if your VPS has a correctly set reverse DNS / PTR record. How you can correctly set the reverse DNS for your IP is visible in a different article on our website.
You can request delisting on http://www.spamrats.com/rats-dyna.php. Please note again that this will only work if you have correctly setup a non-generic reverse DNS record for your IP. Another possible solution is to order an extra IPv4-address for the VPS (or send mail through IPv6), however IP-addresses are allocated randomly based on availability and there is always a chance the new IP address is also located in the blocked IP range.