Public Folder Affinity

When a client must use an alternate server to access public folder content, Exchange utilizes routing groups to calculate the closest available server. The closest available server is determined by a cost property set on the Routing Group connector. The cost for each Routing Group connector is stored in a single cost database that is shared with e-mail routing calculations. Redundant cost tables maintained in previous versions of Exchange are eliminated.

Note   Public Folder affinity applies to all connectors that connect routing groups. This includes:

• Routing Group Connector. This connector always connects two routing groups.
• SMTP Connector. This connector can connect two organizations together, or connect an organization to a foreign system.
• X.400 Connector. This connector can connect two organizations together, or connect an organization to a foreign system.

Public folder affinity is illustrated in the following example.

The client is always connected to its public folder hierarchy server, called Server1. When the client wants to access a message in a public folder, the client attempts to open the folder on Server1. If a replica of this public folder exists on Server1, the user can open the message.

If Server1 does not have a replica of the public folder, it makes a list of all replica servers for the public folder. Server1 then sorts the list in the order of increasing cost, as stored in the cost database. Server1 sends the list to the client. The client then attempts to connect to any one of these servers, starting with the lowest cost first.

Tip   In Exchange 5.5, site affinities were not transitive. For example, if you set up affinity between site1 and site2, and between site2 and site3, you do not automatically get affinity between site1 and site3. In Exchange 2000, affinities are transitive. Within an organization, if all routing groups are connected to allow e-mail to flow, all servers will receive public folder referrals. If a server does not contain replicas of public folders, you can mark specific Routing Group connectors to deny public folder referrals. In this case the client would contact the next server in the referral list.

Public Folder Web Access in a Mixed Environment

In a mixed environment, some public folder or mailbox servers that were running Exchange version 5.5 are upgraded to Exchange 2000. In this mixed environment, if you have clients that use Outlook Web Access (OWA) or a Web browser to access public folders, you should be aware of how public folder referrals work. Web clients access public folders by restricting referrals to Exchange 2000 servers only. The following discussion of public folder referrals applies only to Exchange 2000 Web clients and not MAPI clients or users of Exchange 5.5. OWA.

When a Web client needs a public folder referral, it first contacts the server that hosts the user's private mailbox store. This is done in order to locate the user's default public store. The user's default public store may or may not be on the same server as the user's mailbox store. If the user's default public store is hosted on an Exchange 5.5. server, they will not be able to access public folder content.

If the user's default public store contains a replica of the requested folder, then no referral is required. However, if their default public store is a hierarchy-only server or does not contain a replica of the folder, the server will attempt to redirect the client to another Exchange 2000 server that contains a replica of the folder. If no such server exists, the user will not be able to access that public folder.

To allow an Exchange 2000 user access to a public folder from OWA, the user's default public store must be on an Exchange 2000 server, and there must be a replica of that public folder available an Exchange 2000 server in the organization.

If you follow this guideline, Exchange 2000 OWA users will only be able to access public folder content on Exchange 2000 servers, and not Exchange 5.5. servers. This means that if only a few of your public folder content servers are upgraded, the load caused by Exchange 2000 Web clients will be distributed among the Exchange 2000 servers, and not distributed among Exchange 5.5. servers.