Sadly, at worst they'll get the boot from that provider and move to another provider who they'll be able to use for years more. Even that is difficult as in mos

Sadly, at worst they'll get the boot from that provider and move to another provider who they'll be able to use for years more. Even that is difficult as in most cases providers will accept a "we removed this user" or "no, we never email anyone who hasn't opted in, promise" and come back and tell you they've dealt with it. The only way to actually get rid of it is to mark it as spam and hope enough other people do too that your provider starts treating it as spam for everyone.