Much of the focus on upgrading to Exchange 2000 has to do with upgrading mailbox servers and directories. As you know, however, there are other services and components that make up an Exchange organization. These components are just as necessary to the delivery of messages as the directory and mailbox servers, and their upgrade and deployment must be planned just as carefully.

When upgrading an Exchange Server 5.5 organization to Exchange 2000, the goal of most upgrades is to move messaging and directory data from one system to another without disrupting user availability or performance. Supporting servers, such as connector servers or bridgehead servers, do not have any data to upgrade-so in some cases it may not make sense (or even be necessary) to upgrade a particular server to Exchange 2000. Rather, it's the functionality that needs to be upgraded to Exchange 2000.

For example, if an Exchange Server 5.5 organization has two Exchange 5.5 servers configured with the Internet Mail Service (IMS) to send and receive messages from the Internet, it's not necessary to do an in-place upgrade of those servers-mainly because the Exchange 2000 SMTP connector is very different from the Exchange Server 5.5 IMS. To replace the two IMS servers there would only be one SMTP connector with two bridgehead servers configured. Here you can see that it's the functionality of the IMS that's being upgraded, not the service itself.

Upgrading Connector Servers

As with the example above, other types of connector servers should also be considered for the service they provide and the role they play in the architecture. This is key. If your Exchange 2000 organization has three routing groups connected by routing group connectors, and your Exchange Server 5.5 organization has three sites connected with X.400 connectors using bridgehead servers, the focus should be on how to implement the routing group connectors to connect the routing groups, not how to upgrade the X.400 servers.

Note

When a connector server is upgraded in place, the connectors on that server will also be upgraded. However, there is not a one-to-one correlation between Exchange Server 5.5 connectors and Exchange 2000 connectors. Make sure you understand what an in-place upgrade of a connector server will mean for your organization.

Upgrading Client Access Using Front-end Servers

Another service provided by Exchange Server 5.5 that is very different in Exchange 2000 is Internet client access. Internet clients are those clients that use Internet standard protocols to access mailboxes. These protocols include Post Office Protocol 3 (POP3), Internet Message Access Protocol 4 (IMAP4), Hypertext Transfer Protocol (HTTP), and Network News Transfer Protocol (NNTP). Exchange 2000 has the ability to separate the components that make up a messaging system into different physical servers: front-end servers that manage Internet client requests and back-end servers that store data. In Exchange Server 5.5 Internet clients have to connect directly to the server that hosts the user's mailbox. In Exchange 2000, with front-end servers, the Internet client only needs to connect to the front-end server and the front-end server will pass the requests to the appropriate back-end server. This way, the front-end server can be placed in a demilitarized zone (DMZ) or outside a firewall to provide added security and the Internet client does not need to know the specific mailbox server where their mailbox resides.

Note

MAPI clients, such as Outlook, must connect directly to the mailbox server and cannot use front-end servers. However, Outlook will automatically redirect user profiles if a user mailbox changes from one server to another.

The deployment of front-end servers in an Exchange 2000 organization does not replace any existing servers in an Exchange 5.5 organization. However, users must be made aware of the existence of the front-end servers and how to configure their Internet clients to connect to them. This should be defined in the deployment plan.

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