In a Cisco Unified Communications Manager (CUCM) environment with an SCCP integration, Cisco Unity Connection uses voicemail ports that register to CUCM as SCCP endpoints. The calling privileges for these ports, like any other endpoint, are governed by the Calling Search Space (CSS) assigned to them within CUCM. To prevent fraudulent calls from Unity Connection to the PSTN, an administrator must assign a CSS to the voicemail ports that does not have access to the partition containing the PSTN route patterns. This is the most direct and effective method to block such outbound calls at the call-control level.

A. Routing rules in Unity Connection are for processing incoming calls to direct them to the appropriate mailbox or call handler, not for controlling outbound call permissions.
C. The Rerouting CSS is used for forwarded or redirected calls, not for controlling the originating calling permissions of the device initiating the call, which in this case are the voicemail ports.
D. While Unity Connection restriction tables can limit transfers and notifications, they are configured within Unity Connection itself and are less secure than the fundamental call control provided by CUCM's CSS.

1. Cisco Unified Communications Manager System Configuration Guide

Release 12.5(1)SU1

"Partitions and Calling Search Spaces".

Reference Details: The chapter on "Partitions and Calling Search Spaces" explains that a Calling Search Space assigned to a device (such as an SCCP voicemail port) defines the set of route partitions that the device can call. To restrict access

one must ensure the device's CSS does not include the restricted partition.

2. Security Guide for Cisco Unity Connection Release 12.x

"Preventing Toll Fraud" chapter.

Reference Details: In the section "Restricting Unauthorized Calls from Cisco Unity Connection to the PSTN

" the guide explicitly states: "You can create a partition on Cisco Unified CM that includes only internal numbers and assign it to a calling search space (CSS). You then assign this CSS to the voice-messaging ports that Cisco Unity Connection uses." This directly supports using the voicemail port's CSS as the primary prevention method.

3. SCCP Integration Guide for Cisco Unity Connection Release 12.x

"Setting Up the Cisco Unified Communications Manager for the Integration" section.

Reference Details: This guide details the creation and configuration of voicemail ports in CUCM for the integration. It specifies that each port requires a configuration that includes a Calling Search Space

confirming that this is the standard CUCM mechanism for controlling the ports' call routing capabilities.