sleep 5 is IMHO the shallow end of hackback approaches. As suggested
by hossman returning a clear message to your spammer is an option, largely to disorient or
bloat a bot at the other end. One of many discussions on slashdot
include things like sieving through identified spam , following the 'unsubscribe' links but mangling them to remove
the http://email@example.com to POST large annoying messages to thwart
the good-hit counting.
When all is said and done, doing anything to defend yourself against spam
is joining an arms race. Be careful.
I can't believe it's not psellchecked