Nether.net Open-Relay Blacklist: Any host that sends e-mail to an invalid username @ puck.nether.net or @nether.net is tested to insure that it is not an open-relay. due to the proliferation of spam due to open-relays we have found this to be a necessity. We perform the same tests that are performed if you were to telnet to mail-abuse.org from your mail server. You can check those tests by doing so. It does a reverse-connect to your ip and tests it for a various set of ways that one can send e-mail that would turn out to pass through anti-relaying features.