UM mailbox policies are created in the Configuration container in the Active Directory directory service using the Exchange Management Shell or the Exchange Management Console. By default, a single UM mailbox policy is created every time you create a UM dial plan. The new UM mailbox policy is associated with the UM dial plan and part of the dial plan name is included in the display name of the UM mailbox policy. However, you can create additional UM mailbox policies based on the needs of your organization. Although a single UM mailbox policy is required to enable users for Unified Messaging, you can create additional UM mailbox policies and apply a common set of mailbox policy settings for other groups of users.

Each UM-enabled user's mailbox must be linked to a single UM mailbox policy. After you create a UM mailbox policy, you link one or more UM-enabled mailboxes to the UM mailbox policy. This lets you control PIN security settings such as the minimum number of digits in a PIN or the maximum number of logon attempts for the UM-enabled users who are associated with the UM mailbox policy. If you prefer, you can also control message text settings or dialing restrictions for the same or a different group of UM-enabled mailboxes.

Multiple UM-enabled users can be linked to a single UM mailbox policy. However, a single user can be associated with only one UM mailbox policy. When a user is enabled for Unified Messaging, you must specify an existing UM mailbox policy to be linked to the UM-enabled user's mailbox. After you create a new UM mailbox policy and link it to a UM dial plan, the UM mailbox policy settings defined are then applied to the UM-enabled users. The settings defined on a UM mailbox policy apply only to UM-enabled users to which the UM dial plan is linked and the UM mailbox policy is associated.

The following figure illustrates how UM mailbox policies can be created to control dialing restrictions and PIN security settings for three different groups.