When I tried to send email to users at pacbell.net, my exchange server event log indicates a Event ID: 4089.
Message could not be delivered to 207.115.63.59 (for Pacbell.net). The destination server reported 553 5.3.0 from <IP address of my exchange server> refused by blackhole site input.relays.osirusoft.com
Message could not be delivered to 207.115.63.59 (for Pacbell.net). The destination server reported 553 5.3.0 from <IP address of my exchange server> refused by blackhole site input.relays.osirusoft.com