A perimeter network may be utilized to filter electronic mail messages destined for an internal network. A computer may be utilized to monitor an electronic mail mailbox for changes to a safe recipients list and/or a blocked senders list. The computer may further be utilized to automatically copy the safe recipients list and/or the blocked senders list to a network directory in the internal network. The computer may further be utilized to automatically send the safe recipients list and/or the blocked senders list to a network directory in the perimeter network for utilization by one or more agents executing on a computer in the perimeter network. The one or more agents may be configured to utilize the safe recipients list and/or the blocked senders list to filter electronic mail messages received by the perimeter network which are destined for delivery to the internal network.