You must configure the IP gateways and IP PBXs on your network to communicate with the Exchange 2007 Unified Messaging servers in your Exchange organization. However, you must also configure your Exchange 2007 Unified Messaging server to communicate with the IP gateways and IP PBXs. Exchange 2007 Unified Messaging supports various IP gateway vendors and other vendors of IP PBXs. Each IP gateway is designed to connect to a variety of third-party PBX systems. For more information about how to configure an IP gateway, see How to Configure an IP Gateway or IP PBX for Use with a Unified Messaging Server.

1. Install the Unified Messaging server role. If you are installing the Unified Messaging server role on a separate Exchange 2007 server from the server on which the Mailbox and Hub Transport server roles are installed, use Setup.exe. For more information about how to install the Unified Messaging server role on a separate computer, see How to Perform a Custom Installation Using Exchange Server 2007 Setup. If you are installing the Unified Messaging server role on the Exchange 2007 computer that currently has the Mailbox and Hub Transport server roles installed, you can either use Add or Remove Programs or use Setup.COM. For more information about how to install the Unified Messaging server role on an existing Exchange 2007 computer, see How to Modify an Exchange Installation.
   
   
2. Create and configure a UM IP gateway. For more information about how to manage UM IP gateways, see Managing Unified Messaging IP Gateways.
   
   When you create a UM IP gateway, you can configure the UM IP gateway object to use an IP address or a fully qualified domain name (FQDN). If you use an FQDN you must make sure that you have properly configured a DNS host record for the IP so that the host name will be correctly resolved to an IP address.
   
   A Unified Messaging server will communicate only with IP gateways or IP PBXs that are listed as a trusted Session Initiation Protocol (SIP) peer. In some cases if two IP gateways are configured to use the same IP address, an event with ID 1175 will be logged. Unified Messaging protects against unauthorized requests by retrieving the internal URL of the Unified Messaging Web Services Virtual Directory that is located on the server that has the Client Access role installed and then uses the URL to build the list of FQDNs for the trusted SIP peers. When two FQDNs are resolved to the same IP address this event will be logged.
   
   

   Note:

   You must restart the Microsoft Exchange Unified Messaging (UM) service if an IP gateway is configured to use a fully qualified domain name (FQDN) and the IP gateway's DNS record is changed after the service has been started. If you do not restart the service, the UM server will be unable to locate the IP gateway. This occurs because a UM server maintains a cache for all IP gateways in memory and DNS resolution is performed only when the service is restarted or when an IP gateway's configuration has changed.

   After you install the IP gateway, you must create a UM IP gateway to represent the IP gateway. After you have created a UM IP gateway object, the Unified Messaging server associated with the UM IP gateway will send a SIP OPTIONS request to the IP gateway to ensure that the IP gateway is responsive. If the IP gateway does not respond to the SIP OPTIONS request from the Unified Messaging server, the Unified Messaging server will log an event with ID 1088 stating that the request failed. To resolve this issue, make sure that the IP is available and online and that the Unified Messaging configuration is correct.
   
   
3. Depending on how you create the UM IP gateway, you may also have to create a new UM hunt group. For more information about how to manage UM hunt groups, see Managing Unified Messaging Hunt Groups.
   
   

Note:
After you have connected the UM server to an IP gateway or IP PBX, you must also enable users for Unified Messaging.

• For more information about IP gateways that Exchange Server 2007 supports, see Supported IP Gateways. 
  
  
• For more information about IP PBX and PBX support in Exchange 2007, see IP PBX and PBX Support.
  
  
• For more information about how to configure an IP gateway to connect to a UM server, see How to Configure an IP Gateway or IP PBX for Use with a Unified Messaging Server.
  
  
• For more information about how to configure an IP gateway to connect to a PBX, see How to Configure an IP Gateway to Communicate with a PBX.