The configuration exhibits two critical errors preventing the Message Waiting Indicator (MWI) from functioning.
1. The mwi-server under the sip-ua configuration points to the wrong IP address (172.16.1.254). It must point to the Cisco Unity Express (CUE) module, which, according to the dial-peer's session target, is 172.16.1.253. Additionally, for CUE integration, the unsolicited keyword is mandatory. This keyword allows CUE to send MWI status updates (SIP NOTIFY messages) to CME without a prior subscription request.
2. The ccn subsystem sip configuration is missing the mwi sub-notify command. This command is required to enable the MWI subscription and notification feature within the CME's SIP subsystem, allowing it to process the incoming NOTIFY messages from the CUE MWI server.

A. mwi sip outcall is used to configure MWI notification via an outbound phone call, not for controlling the MWI lamp on a SIP phone.
B. mwi envelop-info is an optional command to include message details in the NOTIFY body; it does not enable the fundamental MWI mechanism.
C. This option corrects neither the incorrect IP address nor the missing unsolicited keyword in the mwi-server command.
E. This option corrects the IP address but incorrectly uses the notify keyword instead of the required unsolicited keyword for CUE integration.

1. Cisco Unified CME and Cisco IOS-XE System Administrator Guide

"Configuring Message Waiting Indication" chapter

"Configuring SIP MWI for Cisco Unity Express on Cisco Unified CME" section.

Page/Section: In the procedure for configuring SIP MWI for CUE

Step 5 specifies the command: mwi-server ipv4:ip-address ... unsolicited. The guide explicitly states

"The unsolicited keyword is required for Cisco Unity Express." This validates option F.

Page/Section: Step 8 in the same procedure specifies the command: mwi sub-notify under the ccn subsystem sip context. This validates option D.

2. Cisco IOS SIP Command Reference

mwi-server command.

Page/Section: Command syntax and usage details explain that the unsolicited keyword configures the gateway to accept unsolicited MWI NOTIFY messages from a voice-mail server

which is the standard operational model for Cisco Unity Express.

3. Cisco Unity Express Configuration Guide

"Configuring Voicemail" chapter

"Message Waiting Indicators" section.

Page/Section: This document describes the MWI mechanism from the CUE perspective

stating: "Cisco Unity Express sends an unsolicited SIP NOTIFY message to Cisco Unified CME to turn the MWI on or off." This confirms that the CME must be configured to accept these unsolicited messages

reinforcing the requirement for the configuration in option F.