Exchange 2003 used several recipient types, but it was often difficult to determine exactly what type a given object was. For example, a mail-enabled user and a mailbox-enabled user looked identical in ADUC without careful inspection. It required opening the user object property pages and inspecting the properties to make the determination.
Even worse, differentiating between mailbox types (i.e. user mailbox from a conference room mailbox) is even more difficult with Exchange 2003 as there is no visual indication of the difference apart from permission settings!
Exchange 2007 solves these problems by adding several explicit Recipient Types which can easily be differentiated by their icon in Exchange Management Console or by looking at the RecipientTypeDetails property on the recipient in Exchange Management Shell.
Exchange 2007 also differentiates all mail-enabled recipients (who can send and receive mail) from non-mail-enabled recipients. Below is a list of the mail-enabled recipient types available in Exchange 2007 and a description of each:
UserMailbox – an Exchange 2007 mailbox assigned to one specific user account in the local forest. Most mailboxes will be of this type unless you are using a Resource Forest.
LinkedMailbox – an Exchange 2007 mailbox in a resource forest assigned to a specific user in the user/account forest.
SharedMailbox – an Exchange 2007 mailbox which is shared by one or more user accounts.
LegacyMailbox – a mailbox located on an Exchange 2000 or Exchange 2003 server.
RoomMailbox – an Exchange 2007 mailbox which represents a conference room for scheduling purposes.
EquipmentMailbox – an Exchange 2007 mailbox which represents a piece of equipment for scheduling purposes (TV, Projector, etc).
MailContact – an AD contact with an external email address assigned
MailForestContact – an AD contact with an external email address assigned that was created by MIIS GALSync. This object represents a recipient object from another forest.
MailUser – this is an AD User with an external email address
MailUniversalDistributionGroup – this is an AD UDG with an email address
MailUniversalSecurityGroup – this is an AD USG with an email address
MailNonUniversalGroup – this is an AD Local or Global Security or Distribution group with an email address
DynamicDistributionGroup – a special group with dynamically generated group membership and an email address.
PublicFolder – a mail-enabled Public Folder
Here is an example of how some of those different types of recipients look like in Exchange 2007 console:
Why make this change?
There were two key reasons for creating these additional recipient types. First, providing explicit recipient types makes it easier for an administrator to quickly differentiate between the different types of recipients. This allows searching, sorting, and filtering by explicit recipient type as well as allowing bulk operation to be managed by recipient type. Second, the recipient type is used directly by the Exchange Management Console to surface different property sets in the GUI. For example you may want to set the capacity of a conference room whereas a standard user mailbox would have no need for this property. With these different recipient types provided, administrators should be able to find and manage mailboxes more quickly and effectively.