These are the features that you'll never see in the version of rblcheck
that I produce (rblcheck is GPL; you're free to produce your own version
if this doesn't suit you well), and the rationale behind why not.

Support for doing lookups of FQDNs: This is a futile method of checking
    whether a particular system is blackholed; if the originating system
    has control of reverse DNS for their IP space, they can make their IP
    address resolve to anything they want, such as system.network.com. If
    rblcheck were to do a lookup on that, "system.network.com" might
    resolve to anything (such as "127.0.0.1, which will always pass with
    every currently known RBL-based blacklist).
