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Chapter 1: Introducing Exchange 2000 Server
...The Organization of an Exchange EnvironmentIn previous versions of Exchange Server, each group of Exchange servers was known as a site, and each site defined the group's boundaries for both administration and routing. Exchange 2000 Server does away with sites and instead allows Exchange servers to be grouped into administrative groups and routing groups. This split allows administrators to deploy their organizations along boundaries that are more closely aligned with the real world than was previously possible. In addition, the integration of Exchange 2000 Server with the Microsoft Windows 2000 Active Directory directory service has brought about changes in the way the various recipients are managed. This section outlines the basic organizational features of Exchange 2000 Server.
An administrative group is a collection of Exchange servers and administrative objects that are logically grouped together for common administrative purposes. For example, your organization might have two system administrators, one responsible for administering collaborative services and the other responsible for administering servers and connectors. You could use administrative groups as a way of assigning permissions and policies to each administrator. An administrative group can contain policies, routing groups, public folder trees, servers, and more.
A routing group is a collection of Exchange servers that are all physically connected by a permanent, high-speed, reliable network. A server is contained within one-and only one-routing group. The routing group is the closest thing to a site in previous versions of Exchange Server. Messages sent between servers in a routing group are delivered directly from source to destination. Messages sent between servers in different routing groups must be routed through bridgehead servers, servers that are specifically designated to route messages from one routing group to another over specialized connectors.
Policies are another feature new to Exchange 2000 Server. Policies are collections of configuration settings that are applied to one or more Exchange configuration objects. For example, an administrator could configure a set of parameters to govern a certain aspect of server behavior and then assign those parameters, as a policy, across tens or even hundreds of servers. Once policies are implemented, changes to the policies affect all objects to which the policies are assigned, making it easy to change the configuration of entire groups of objects at a stroke. Exchange 2000 Server uses two basic types of policies: system policies and recipient policies.
System policies are used to configure servers and the message store databases on those servers. Three classes of system policies are defined: mailbox store policies, public folder store policies, and server policies. A system policy defines configuration settings for a class of objects (such as public folders). Once you have defined a policy, you can apply it to existing objects or create new objects using that policy. You can then change the configuration for all of those objects with one stroke. For example, you might create a system policy that limits the size of messages that can be posted to a group of public folders. Once that policy has been applied to those folders, you could change the limits at any time for all of the folders simply by changing the policy.
Recipient policies are used to configure objects such as users, mailboxes, groups, and contacts-objects typically associated with the user side of the system. Because much of this directory information resides in the Windows 2000 Active Directory, recipient policies actually apply settings to the Windows 2000 domain containers. Recipient policies work in much the same way that system policies do. You can use them to apply and modify configuration settings to groups of recipients all at once. For example, you might configure a recipient policy that defines how an SMTP address is created for certain recipients. Once that policy has been applied, you can change the addressing scheme for all of the recipients by changing the policy.
Server is the term used in the Microsoft Exchange topology to refer to an individual computer that has the Microsoft Exchange Server messaging application installed and running on it. The name of the server is typically the same as the name of the Windows 2000 computer that hosts the Exchange Server application.
There are no hard and fast rules as to how many servers you should have within a particular routing group. The size of the machine acting as the server will have some bearing on how many users and how large a store the machine can support. In addition, you should put some thought into which servers to place users on. When individual users on the same server communicate through Exchange Server, they do not add to network bandwidth because the message does not need to move across the network between separate physical machines. By grouping users according to how they interact with one another, you can improve the Exchange server's performance and even the performance of the entire messaging system.
Although the recipient is the lowest level of the Exchange hierarchy, it is a critical component of the Exchange organization. As the name implies, a recipient is an entity that can receive an Exchange message. Most recipients are associated with a single, discrete mailbox, although this mailbox can be represented by several addresses, depending on the addressing types implemented within Exchange.
In previous versions of the Exchange Server, a separate tool-the Exchange Administrator-was used to create recipients and to associate them with Microsoft Windows NT user accounts. With the introduction and integration of Windows 2000 Server and Exchange 2000 Server, all that has changed. When you install Exchange 2000 Server, it adds Exchange-related functionality to the Windows 2000 Active Directory Users and Computers snap-in. This tie to Active Directory means that, in addition to mailboxes, Exchange 2000 Server supports other types of recipients, including groups and contacts.
Mailboxes A mailbox is an area of an Exchange Server's mailbox store database where a particular user's private messages are stored. A Windows 2000 user object that has been given a mailbox is referred to as mailbox enabled. Only user objects can be mailbox enabled.
Note: You can make other objects participate in Exchange 2000 Server routing simply by giving them an e-mail address. Such objects are referred to as mail enabled and are not associated with an actual mailbox.
Groups A group is a collection of users, contacts, and even other groups that is able to receive messages. When a group receives a message, Exchange Server sends a copy of the message to each of the recipients within the group. The term group also refers to a Windows 2000 security object that is a collection of users and other groups. An Exchange 2000 Server group is always based upon a Windows 2000 group. A group is the functional equivalent of a distribution list in previous versions of Exchange Server.
Contacts A contact is a Windows 2000 object that is not an actual user and thus cannot log on to the network. Contacts can receive e-mail from Exchange users, just as standard Exchange recipients can, after their addresses are defined in the Exchange system's Global Address List. Through the use of contacts, you can integrate external recipients, such as Internet e-mail addresses, into the address list of your Exchange system. Contacts are the functional equivalent of custom recipients in previous versions of Exchange Server.
An address list is simply a list of recipients. The Global Address List is the list of all Exchange Server recipients in the entire Exchange organization. Exchange Server uses address lists to hold and organize the names of the recipients associated with the system.
An Exchange system can have hundreds of thousands of recipients, making it difficult for a user to locate an individual recipient's name. In addition, e-mail addresses can be somewhat cryptic. Various legacy messaging systems have restrictions on the length of the user's mailbox name, and some administrators assign puzzling mailbox names. All in all, it can be difficult to guess a user's e-mail address. The primary purpose of an address list, from a user's point of view, is to provide a way to locate an e-mail address for a recipient. When the administrator of an Exchange environment creates a recipient, the person's name-not a cryptic e-mail address-shows up in the Global Address List, making it easier for Exchange users to locate and send mail to recipients.
In addition to the Global Address List maintained by Exchange Server, individual users can create their own personal address lists, called address books. Personal address books can contain a portion of the Global Address List, as well as other custom addresses added by the user, to make it easier to access the addresses they use most frequently.
You should understand one more piece of the Exchange Server topology before moving on: connectors. A connector is a piece of software that acts as a gateway between Exchange Server routing groups or from a routing group to a nonExchange mail system (such as foreign X.400 messaging systems). A connector enables the Exchange system to interact directly with a foreign e-mail system, as though its users were part of your Exchange system. Connectors can integrate foreign address lists into the Global Address List, enable message exchange, provide access to shared messaging folders, and make other functions available. Some connectors simply enable a consistent mail-forwarding and receipt operation. In addition to providing a link between Exchange Server and other messaging systems, a connector can be extremely useful if you are in the process of migrating to Exchange Server or connecting to nonmessaging systems such as fax or voice mail...