IP phone users report that the MWI light does not work while receiving VM messages. Which action must be taken to troubleshoot this issue?

User mailbox size affects the ability to receive new messages but does not influence the MWI signaling mechanism or the light status on the phone.

The Port Activity Report in Cisco Unity Connection logs all port-level activity, including MWI on/off requests sent to CUCM. Running this report allows an engineer to verify whether Unity Connection is attempting to set MWI and whether the requests are succeeding or failing, directly isolating where in the signaling path the breakdown occurs.

Resetting the MWI function in Unity Connection is a corrective action, not a troubleshooting step - it should only be performed after the Port Activity Report identifies a problem.

Resetting the IP phone may temporarily clear a stale MWI state on that one device but does not diagnose or resolve a systemic MWI delivery failure.