XENOPHONZ wrote "If I understand the matter correctly, IP bans have the effect of locking out an entire section of IP's -- not just the IP held by the banned individual.". Similar happened with me. I worked in a university until recently. (I am now retired.) Around 10 or 15 years ago the university's email server blocked all access to sites whose names contained "netcom", to block access to some porn sites. And as a side-effect it blocked incoming email from a small computer-repair firm called Netcom that I needed to contact sometimes.