Global address list (GAL) segmentation (also known as GAL segregation) is the process whereby you segment users into specific groups to provide customized views of your organization’s GAL. In Exchange Server 2007 and earlier, segmenting the GAL was complicated, requiring you to use either a Query Base DN (which acted as a root for directory searches) or access control lists (ACLs) to allow or deny access to each address list.

To simplify the process, Exchange 2010 Service Pack 2 (SP2) introduces address book policies (ABPs). When creating an ABP, you assign a GAL, an offline address book (OAB), a room list, and one or more address lists to the policy. You can then assign the ABP to mailbox users, providing them with access to a customized GAL in Outlook and Outlook Web App. The goal is to provide a simpler mechanism to accomplish GAL segmentation for on-premises organizations that require multiple GALs.

To learn more about ABPs, see Understanding Address Book Policies.

When users want to use their client application to find recipient information, they can select from available address lists. Several address lists, such as the global address list (GAL), are created by default. Exchange contains the following default address lists, which are then automatically populated with new users, contacts, groups, or rooms as they're added to your organization:

• All Contacts   This address list contains all mail-enabled contacts in your organization. Mail-enabled contacts are those recipients who have an external e-mail address. If you want mail-enabled contact information to be available to all users in your organization, you must include the contact in the GAL. To learn more about mail contacts, see Understanding Recipients.
  
  
• All Groups   This address list contains all mail-enabled groups in your organization. Mail-enabled groups are groups of recipients that are created to expedite the mass sending of e-mail messages and other information. When an e-mail message is sent to a mail-enabled group, all members of that list receive a copy of the message. To learn more about mail-enabled groups, see Understanding Recipients.
  
  
• All Rooms   This address list contains all resources that have been designated as a room in your organization. Rooms are resources in your organization that can be scheduled by sending a meeting request from a client application. The user account that's associated with a room is disabled. For instructions about how to add resource mailboxes to an address list, see Add Resource Mailboxes to an Address List. To learn more about resource mailboxes, see Understanding Recipients.
  
  
• All Users   This address list contains all mail-enabled users in your organization. A mail-enabled user represents a user outside your Exchange organization. Each mail-enabled user has an external e-mail address. All messages sent to mail-enabled users are routed to this external e-mail address. A mail-enabled user is similar to a mail contact, except that a mail-enabled user has Active Directory logon credentials and can access resources. To learn more about mail-enabled users, see Understanding Recipients.
  
  
• Default Global Address List   This address list contains all mail-enabled users, contacts, groups, or rooms in the organization. During setup, Exchange creates various default address lists. The most familiar address list is the GAL. By default, the GAL contains all recipients in an Exchange organization. In other words, any mailbox-enabled or mail-enabled object in an Active Directory forest that has Exchange installed is listed in the GAL. For ease of use, the GAL is organized by name, not by e-mail address. For more information, see Managing Address Lists.
  
  
• Public Folders   This address list contains all public folders in your organization. Access permissions determine who can view and use the folders. Public folders are stored on computers running Exchange. For more information about public folders, see Managing Public Folders.
  
  

An Exchange organization can contain thousands of recipients. If you compile all your recipients in the default address lists, those lists could become quite large. To prevent this, you can create custom address lists to help users in your organization find what they are looking for more easily.

For example, consider a company that has two large divisions and one Exchange organization. One division, named Fourth Coffee, imports and sells coffee beans. The other division, Contoso, Ltd, underwrites insurance policies. For most day-to-day activities, the employees at Fourth Coffee don't communicate with the employees at Contoso, Ltd. Therefore, to make it easier for employees to find recipients who exist only in their division, you can create two new custom address lists—one for Fourth Coffee and one for Contoso, Ltd. When searching for recipients in their division, these custom address lists allow employees to select only the address list that's specific to their division. However, if an employee is unsure about the division in which the recipient exists, the employee can search within the GAL, which contains all recipients in both divisions.

You can also create subcategories of address lists called hierarchical address lists. For example, you can create an address list that contains all recipients in Manchester and another that contains all recipients in Stuttgart.

Although address lists are useful tools for users, poorly planned address lists can cause frustration. To make sure that your address lists are practical for users, consider the following best practices:

• Avoid creating so many address lists that users won't be sure which list to search for recipients.
  
  
• Name your address lists in such a way that, when users glance at them, they will know immediately which recipient types are contained in the list. If you have difficulty naming your address lists, create fewer lists and remind users that they can find anyone in your organization by using the GAL.
  
  

For detailed instructions about creating an address list, see Create an Address List.