I try to figure out which IP is a residential proxy. The most IP's with a fraud score +75 has an open port 25.
A normal visitor's IP does not have port 25 open.
So you can assume that it is a configured IP address, right.
My questions
Is there a relatively reliable way to expose a residential proxy IP if that IP is using/opening port 25?
Is it possible to query an IP that calls a webstei directly on an open port 25 and then block it accordingly. ....IF ip-port_25=true THAN add_to_htaccess_blacklist; ?