rblcheck 1.5

rblcheck is a lightweight C program for doing checks against Paul Vixies MAPS Blackhole List and the ORBS open relay list. It works well in conjunction with Procmail for filtering unwanted and spamming bulk email.
The general idea behind RBL-style listings is rapid lookup of IP addresses using DNS (for example, for blacklisting IP addresses because of abuse). Each IP address is reversed and has a domain name attached to it; for example, the IP address 127.0.0.2 would become 2.0.0.127, and then a domain such as "relays.visi.com" would be added to it. You would then try to resolve the result (ie. 2.0.0.127.relays.visi.com); if you receive a positive reply, then you know that the address is listed. Further information can also be queried, such as text descriptions of why the address was listed.
Enhancements:
- Converted to automake/autoconf for configuration, which should make it easier to extend portability
- Added support for checking multiple addresses in one invokation.
- Added support for reading addresses to check from standard input, by specifying an argument of -.
- Changed rbl.dorkslayers.com to relays.orbs.org, due to a change in management.