A comprehensive UBE strategy should include both ways to prevent users from receiving UBE (access controls, mailbox filtering, address verification, RBL) as well as preventing users from unauthorized relay of mail from your system to other systems. This second method is called relay blocking. In its simplest form, relay blocking is achieved by enabling local users and systems to relay mail while rejecting relay attempts from non-local systems. Using IP addresses as the differentiator easily and securely makes this differentiation between local versus non-local. By default, Messaging Server enables relay blocking upon installation. See Configuring Anti-Relaying with Mapping Tables for more information.