REFERENCE
Description: Use this setting to determine whether all hosts should be subject to the anti-spam controls specified for the server.
1 - Internal hosts included for anti-spam controls.
Default: In the absence of the setting, any internal hosts would be exempt from the controls.
UI equivalent: In the server's Configuration Settings document, first click the Router/SMTP tab, then the Restrictions and Controls tab, and finally the SMTP Inbound Controls tab. In the Inbound Relay Enforcement section's "Perform Anti-Relay enforcement for these connecting hosts" field, select "All connecting hosts" or "External hosts."
See also