Exchange uses the Recipient Update Service primarily to generate and update default and customized address lists, and to process changes made to recipient policies. This service makes sure that when new recipient policies or address lists are created, their content is applied to the appropriate recipients in the organization. The Recipient Update Service also applies existing policies to new recipients that are created after the policy or address list has already been established. In this way, information is kept current with minimal administrative overhead.

You must have at least one Recipient Update Service for each domain in your organization, and it must be run from an Exchange 2003 or Exchange 2000 server. For domains that do not have these Exchange servers, the Recipient Update Service must be run from an Exchange server outside the domain. You can set up more than one Recipient Update Service for a domain, if there are multiple domain controllers. Each Recipient Update Service must read from and write to a unique domain controller.
If you do not have a Recipient Update Service for a domain, you cannot create recipients in that domain.

In situations where you have high network latency in a domain, set up the Recipient Update Service at the local sites. For example, if you have one domain that has sites in Seattle and in Beijing, there might be a long delay before a mailbox that an administrator creates in Beijing is processed by the Recipient Update Service in Seattle. In this case, having a Recipient Update Service on the local domain controller in Beijing will decrease the time the user has to wait to be able to access the mailbox after it has been created. For detailed instructions on creating a new Recipient Update Service, see How to Create a New Recipient Update Service.

You can choose to have the Recipient Update Service run at customized intervals. By default, the Recipient Update Service is set to Always Run, and when it runs, only required changes are made. Changes are necessary when a recipient, recipient policy, or address list is changed or created. Any changes that have occurred since the last time the Recipient Update Service ran are applied. For detailed instructions, see How to Change the Update Interval of the Recipient Update Service.