I've noticed a dramatic increase in the number of bad email addresses on my list that come from an IP address range like
(All of these are from China by the way which is not a target market for me)
When they sign up they are using seeming good email addresses at known domains like firstname.lastname@example.org, etc. and they always come up with unique addresses so I cannot ban by domain (obviously) nor can I ban by email address since each new one is unique.
However since they are ALL originating from a known IP address range it would be very helpful if I could ban by IP address.