Mailboxes are the most common recipient type used by information workers in an Exchange organization. Each mailbox is associated with an Active Directory user account. The user can use the mailbox to send and receive messages, and to store messages, appointments, tasks, notes, and documents. Mailboxes are the primary messaging and collaboration tool for the users in your Exchange organization.

Mailbox components

Each mailbox consists of an Active Directory user and the mailbox data that's stored in the Exchange mailbox database (as shown in the following figure). All configuration data for the mailbox is stored in the Exchange attributes of the Active Directory user object. The mailbox database contains the actual data that's in the mailbox associated with the user account.

Important:
When you create a mailbox for a new or existing user, the Exchange attributes required for a mailbox are added to the user object in Active Directory. The associated mailbox data isn't created until the mailbox either receives a message or the user signs in to it.

Mailbox components

Warning:
If you remove a mailbox, the mailbox data stored in the Exchange mailbox database is marked for deletion and the associated user account is also deleted from Active Directory. To retain the user account and delete only the mailbox data, you must disable the mailbox.

Mailbox types

System mailboxes

Planning for mailboxes

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:
Note the terminology differences between Active Directory and Exchange. In Active Directory, a distribution group refers to any group that doesn't have a security context, whether it's mail-enabled or not. In Exchange, all mail-enabled groups are referred to as distribution groups, whether they have a security context or not.

Exchange supports the following types of distribution groups:

• Distribution groups   These are Active Directory universal distribution group objects that are mail-enabled. They can be used only to distribute messages to a group of recipients.
  
  
• Mail-enabled security groups   These are Active Directory universal security group objects that are mail-enabled. They can be used to assign 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. 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 aren't universal groups. These groups can still be managed by using the EAC or the Shell.
  
  

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

Dynamic distribution groups 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 email message is sent to a dynamic distribution group, it's 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, you can use precanned filters. A precanned filter is a commonly used 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
  
  
• Recipient container
  
  

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

Mail contacts typically contain information about people or organizations that exist outside your Exchange organization. Mail contacts can appear in your organization’s shared address book (also called the global address list or GAL) and other address lists, and can be added as members to distribution groups. Each contact has an external email address, and all email messages that are sent to a contact are automatically forwarded to that address. Contacts are ideal for representing people external to your Exchange organization (in the shared address book) who don't need access to any internal resources. The following are mail contact types:

• Mail contacts   These are mail-enabled Active Directory 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 directory synchronization. Mail forest contacts are read-only recipient objects that can be updated or removed only by means of synchronization. You can't use Exchange management interfaces to modify or remove a mail forest contact.
  
  

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

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 addresses.

Another scenario is to create mail users in your organization for users who you don't 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 EAC, you use the Recipients > Contacts page to create and manage mail users. There isn't a separate page for mail users.

Public folders are intended to serve as a repository for information 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 email messages to, and sometimes receive email messages from, the public folder. Each mail-enabled folder has an object in Active Directory that stores its email address, address book name, and other mail-related attributes.

You can manage public folders by using either the EAC or the Shell. For more information about managing public folders, see Public Folders.

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 Exchange.

The Microsoft Exchange recipient isn't a typical recipient object, such as a mailbox, mail user, or mail contact, and it isn't managed by using the typical recipient tools. However, you can use the Set-OrganizationConfig cmdlet in the Shell to configure the Microsoft Exchange recipient.

Note:
When system-generated messages are sent to an external sender, the Microsoft Exchange recipient isn't used as the sender of the message. Instead, the email address specified by the ExternalPostmasterAddress parameter in the Set-TransportConfig cmdlet is used.