And thus we now have blacklist entries such as:
barracuda1.aus.texas.net
barracuda.yale-wrexham.ac.uk
barracuda.morro-bay.ca.us
barracuda.ci.mtnview.ca.us
barracuda.elbert.k12.ga.us
barracuda.fort-dodge.k12.ia.us
barracuda.ci.garner.nc.us
barracuda.ship.k12.pa.us
and many, many more.
Blocking based on rDNS simply because it implies that a certain piece of
equipment is at that address is... not advisable.