You have an Exchange Server 2013 organization that has Unified Messaging (UM) enabled for all mailboxes. The organization is configured to use an IP gateway to connect to a legacy PBX. An administrator recently performed some configuration changes. After the changes, users report that their voice mail is no longer being delivered to their Exchange Server mailbox. The users do not report any other problem. You need to identify which configuration change causes the issue. Which cmdlet should you run?