Exchange 2007 supports the following mailbox types:

• User mailbox   User mailboxes are assigned to individual users in your Exchange organization. User mailboxes provide your users with a rich collaboration platform. They can send and receive messages, manage their contacts, schedule meetings, and maintain a task list. Users can also have voice mail messages delivered to their mailboxes. User mailboxes are the most commonly used mailbox type, and it is typically the mailbox type that is assigned to users in your organization.
  
  
• Linked mailbox   Linked mailboxes are mailboxes that are accessed by users in a separate, trusted forest. Linked mailboxes may be necessary for organizations that choose to deploy Exchange in a resource forest. The resource forest scenario allows an organization to centralize Exchange in a single forest, while allowing access to the Exchange organization with user accounts in one or more trusted forests. For more information about deploying Exchange in a resource forest topology, see the following topics:
  
  
  • Planning for a Complex Exchange Organization
    
    
  • How to Deploy Exchange 2007 in an Exchange Resource Forest Topology
    
    
  As stated in the "Mailbox Components" section earlier in this topic, every mailbox must have a user account associated with it. However, the user account that will access the linked mailbox does not exist in the forest where Exchange is deployed. Therefore, a disabled user account that exists in the same forest as Exchange is associated with each linked mailbox. Figure 2 shows the relationship between the linked user account that will be used to access the linked mailbox and the disabled user account in the Exchange resource forest that is associated with the linked mailbox.
  
  
  
  

  Figure 2   Linked mailbox

• Shared mailbox   Shared mailboxes are mailboxes that are not primarily associated with individual users and are generally configured to allow logon access for multiple users.
  
  Although it is possible to grant additional users the logon rights to any mailbox type, shared mailboxes are dedicated for this functionality. The Active Directory user that is associated with a shared mailbox must be a disabled account. After a shared mailbox is created by using the command line in the Exchange Management Shell, you must grant permissions to all users that require access to the shared mailbox.
  
  

  Important:

  You can only use the Exchange Management Shell to manage shared mailboxes. Managing includes tasks such as creating, removing, enabling, disabling, and so on. After a shared mailbox has been created, you can use the Exchange Management Console to do some tasks such as viewing, modifying or moving the shared mailboxes. We recommend that you use resource mailboxes or Microsoft SharePoint Portal Server portals for collaboration instead of shared mailboxes. To learn more about converting a shared mailbox to a resource mailbox, see How to Convert a Mailbox.

• Legacy mailbox   Legacy mailboxes are mailboxes that reside on servers running Exchange 2003 or Exchange 2000. You can manage legacy mailboxes by using the Exchange Management Console or the Exchange Management Shell. However, not all Exchange 2007 features will apply to these mailboxes. 
  
  For more information about using Exchange 2007 with Exchange 2003 or Exchange 2000, see Coexisting with Exchange Server 2003 and Exchange 2000 Server.
  
  
• Room and equipment mailbox   Resource mailboxes are special mailboxes that are designed to be used for scheduling resources. Like all mailbox types, a resource mailbox has an associated Active Directory user account, but it must be a disabled account.
  
  There are two types of resource mailboxes available in Exchange 2007:
  
  
  • Room mailboxes   These are resource mailboxes that are assigned to meeting locations, such as conference rooms, auditoriums, and training rooms.
    
    
  • Equipment mailboxes   These are resource mailboxes that are assigned to non-location specific resources, such as portable computer projectors, microphones, or company cars.
    
    
  You can include both types of resource mailboxes as resources in meeting requests, providing a simple and efficient way to utilize resources for your users. You can configure resource mailboxes to automatically process incoming meeting requests based on the resource booking policies that are defined by the resource owners. For example, you can configure a conference room to automatically accept incoming meeting requests except recurring meetings, which can be subject to approval by the resource owner. To learn more about using resource mailboxes, see Managing Resource Scheduling.
  
  

To help provide a rich collaboration platform for mailbox users, Exchange 2007 includes the following new and improved mailbox features:

• Unified Messaging   Exchange 2007 introduces Unified Messaging (UM) for mailbox users. UM combines voice messaging, fax, and e-mail messaging into a single messaging infrastructure. UM puts all e-mail, voice, and fax messages into Exchange 2007 mailboxes that can be accessed from a variety of devices. After Exchange 2007 UM servers have been deployed on the network, users can access their messages from a telephone by using Microsoft Outlook Voice Access, from a mobile device, or from the computer of a user who is running Microsoft Windows XP. To learn more about UM in Exchange 2007, see New Unified Messaging Functionality.
  
  
• New and improved client functionality     Exchange 2007 provides new and improved ways for users to access their mailboxes. To learn more about new and improved client features, see New Client Functionality.
  
  
• Information worker functionality   Exchange 2007 includes several feature and functionality improvements in the information worker area. These include improvements and enhancements to calendaring, resource management, the Out of Office feature, and messaging records management (MRM). To learn more about the new information worker features, see New Information Worker Functionality.
  
  

Mailboxes are created in mailbox databases on Exchange servers that have the Mailbox server role installed. To help provide a reliable and effective platform for your mailbox users, detailed planning for the deployment of Mailbox servers and databases is essential. To learn more about planning for Mailbox servers and databases, see the following topics:

• Planning Your Deployment
  
  
• Planning for Mailbox Servers
  
  
• Managing Mailbox Databases
  
  
• Managing Mailbox Features
  
  

Distribution groups are mail-enabled Active Directory group objects that are primarily used for distributing messages to multiple recipients. Any recipient type can be a member of a distribution group.

Important:
It is important to note the terminology differences between Active Directory and Exchange 2007. In Active Directory, a distribution group refers to any group that does not have a security context, whether it is mail-enabled or not. In contrast, in Exchange 2007, all mail-enabled groups are referred to as distribution groups, whether they have a security context or not.

Exchange 2007 supports the following types of distribution groups:

• Mail-enabled universal distribution groups   These are Active Directory distribution group objects that are mail-enabled. They can be used only to distribute messages to a group of recipients.
  
  
• Mail-enabled universal security groups   These are Active Directory security group objects that are mail-enabled. They can be used to grant access permissions to resources in Active Directory and can also be used to distribute messages.
  
  
• Mail-enabled non-universal groups   These are Active Directory global or local group objects that are mail-enabled. In Exchange 2007, you can create or mail-enable only universal distribution groups. You may have mail-enabled groups that were migrated from previous versions of Exchange that are not universal groups. These groups can still be managed by using the Exchange Management Console or the Exchange Management Shell.
  
  

  Note:
  To convert a domain-local or a global group to a universal group, you can use the Set-Group cmdlet in the Exchange Management Shell. For more information, see Set-Group.

Dynamic distribution groups (known as query-based distribution groups in Exchange 2003) are distribution groups whose membership is based on specific recipient filters rather than a defined set of recipients.

Unlike regular distribution groups, the membership list for dynamic distribution groups is calculated each time a message is sent to them, based on the filters and conditions that you specify. When an e-mail message is sent to a dynamic distribution group, it is delivered to all recipients in the organization that match the criteria defined for that dynamic distribution group.

Important:

A dynamic distribution group includes any recipient in Active Directory that has attributes that match the group's filter at the time a message is sent. If a recipient's properties are modified to match the group's filter, that recipient could inadvertently become a group member and start receiving messages that are sent to the dynamic distribution group. Well-defined, consistent account provisioning processes can reduce the chances of this issue occurring.

To help you create recipient filters for dynamic distribution groups, Exchange 2007 provides precanned filters. A precanned filter is a commonly used Exchange 2007 filter that you can use to meet a variety of recipient-filtering criteria. You can use these filters to specify the recipient types that you want to include in a dynamic distribution group. In addition, you can also specify a list of conditions that the recipients must meet. You can create precanned conditions based on the following properties:

• Custom attributes 1–15
  
  
• State or province
  
  
• Company
  
  
• Department
  
  

You can also specify conditions based on recipient properties other than those previously listed. To do this, you must use the Exchange Management Shell to create a custom query for the dynamic distribution group. Keep in mind that the filter and condition settings for dynamic distribution groups that have custom recipient filters can be managed only by using the Exchange Management Shell. For an example of how to create a dynamic distribution group by using a custom query, see How to Create a New Dynamic Distribution Group.

Note:
In the Exchange Management Console, you use the Distribution Group node under Recipient Configuration to manage dynamic distribution groups. There is not a separate node for dynamic distribution groups.

Mail contacts typically contain information about people or organizations that exist outside your Exchange organization. Mail contacts can appear in the global address list (GAL) and other address lists, and can be added as members to distribution groups. Each contact has an external e-mail address, and all e-mail messages that are sent to a contact are automatically forwarded to that address.

Exchange 2007 supports the following types of mail contacts:

• Mail contacts   These are mail-enabled Active Directory directory service contacts that contain information about people or organizations that exist outside your Exchange organization.
  
  
• Mail forest contacts   These represent recipient objects from another forest. These contacts are typically created by MIIS synchronization. Mail forest contacts are read-only recipient objects that can be updated or removed only by means of synchronization. You cannot use Exchange management interfaces to modify or remove a mail forest contact.
  
  

Contacts are ideal for representing people external to your Exchange organization who do not need access to any internal resources.

Mail users are similar to mail contacts. Both have external e-mail addresses, both contain information about people outside your Exchange organization, and both can be displayed in the GAL and other address lists. However, unlike a mail contact, mail users have Active Directory logon credentials and can access resources to which they are granted permission.

If a person external to your organization requires access to resources on your network, you should create a mail user instead of a mail contact. For example, you may want to create mail users for short-term consultants who require access to your server infrastructure, but who will use their own external e-mail addresses.

Another scenario is to create mail users in your organization for whom you do not want to maintain an Exchange mailbox. For example, after an acquisition, the acquired company may maintain their separate messaging infrastructure, but may also need access to resources on your network. For those users, you may want to create mail users instead of mailbox users.

Note:
In the Exchange Management Console, you use the Mail Contact node under Recipient Configuration to manage mail users. There is not a separate node for mail users.

Public folders are intended to serve as a repository for information that is shared among many users. Mail-enabling a public folder provides an extra level of functionality to users. In addition to being able to post messages to the folder, users can send e-mail messages to, and sometimes receive e-mail messages from, the public folder. Each mail-enabled folder has an object in Active Directory that stores its e-mail address, address book name, and other mail-related attributes.

You can manage public folders by using either the Exchange Management Shell or the Public Folder Management Console. To access the Public Folder Management Console, click the Toolbox node in the Exchange Management Console. For more information about managing mail-enabled public folders, see How to View or Configure the Settings of Mail-Enabled Public Folders.

Note:
To use the Public Folder Management Console to manage public folders, you must have Exchange Server Service Pack 1 (SP1) installed.

The Microsoft Exchange recipient is a special recipient object that provides a unified and well-known message sender that differentiates system-generated messages from other messages. It replaces the “System Administrator” sender that was used for system-generated messages in earlier versions of Microsoft Exchange Server.

The Microsoft Exchange recipient isn't a typical recipient object, such as a mailbox, mail user, or mail contact. It isn't managed by using the typical recipient tools. However, you can use the Set-OrganizationConfig cmdlet in the Exchange Management Shell to configure the Microsoft Exchange recipient. For more information about managing the Microsoft Exchange Recipient, see Managing the Microsoft Exchange Recipient.

Note:
When system-generated messages are sent to an external sender, the Microsoft Exchange recipient is not used as the sender of the message. Instead, the e-mail address that is specified by the ExternalPostmasterAddress parameter in the Set-TransportServer cmdlet is used. For more information about the external postmaster address, see Managing the External Postmaster Address.