Changes since 20190930:

Marco d'Itri <md@linux.it> forked the original unmaintained code.

Cleaned up the source code by updating obsolete language constructs
and removing compatibility code for obsolete systemd.

The documentation still needs to be updated to reflect most changes.

Replaced "RBL" with "DNSBL" in user-visible messages.

Added support for IPv6 DNSBLs.

Added support for domain-based DNSBLs (URIBLs).

Changes since 1.4:

- 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 '-'.

- Updated sites.h to mesh with current reality (almost ALL of the sites
  listed had changed since the last update). Added a recommendation that
  distribution maintainers NOT enable any of the listings by default.

- Converted documentation to docbook, with a script for automatically
  generating html, ps, and rtf formats.

- Added an RPM spec file.

Changes since 1.3:

- Fixed output bug with some odd combinations of -q and -t.

- Added T_TXT and PACKETSZ definitions in the event that some systems
  might not define them.

- Fixed error with return values not matching the advertised values.

- Fixed bug with rbl.dorkslayers.com's tendancy to use CNAMEs for
  everything.

- Added support to dynamically grow the buffer used by res_query(), so
  that we can always support whatever the RBLs send back to us.

- Minor documentation fixes.

Changes since 1.2:

- New feature: the ability to query multiple RBL-alike services in
  one invokation.

- New command-line option: -l (list known RBL services)

- New command-line option: -s <service> (toggle an RBL service)

- New command-line option: -c (clear the list of RBL services)

- Compat-buster: formatting of the output has changed slightly, to
  accomodate multiple RBL services. The new output includes the name
  of the server currently being checked (ie. "RBL filtered by ..."),
  and there can be multiple outputs of "(not) RBL filtered by ...".

- Added a very basic "install" target to the Makefile.

- Some generalization of the code.

Changes since 1.1:

- a bunch of portability fixes, plus some minor code cleanup to make
  things a little more comfortable on multiple platforms. Should now
  compile on K&R-only systems, and on machines with wierd resolver
  libraries.

Changes since 1.0:

- clarified the procmail recipe in INSTALL to include some logic to
  prevent problems with local email if the system rblcheck is running
  on has actually been blacklisted.

- Noticed a glaring error in QMail support: TCPREMOTEIP is NOT passed
  on to .qmail-executed programs. Damn.

- added origip.c and origip.awk to obtain the sender's IP address from
  QMail headers.

- added "docs" and "utils" directories to organize things a bit better.

- added "extern int optind;" to make some platforms a little happier.

- fixed compilation on NeXT.

- added some useful usage output, and added a '-v' flag for version info.

- added a '-t' flag for displaying of TXT RRs.
