See the list here: http://www.braemoor.co.uk/robotreport.php
It might be counter-productive to block all. But rogue mail harvesters as such. What criteria are there?
See for instance: http://www.projecthoneypot.org/ip_119.63.213.123
Here you see harvesters arranged by last bad event: http://www.projecthoneypot.org/list_of_ips.php?t=h
Like to hear your views on this?
polonus