Public Folder Referrals

When a client attempts to connect to a public folder, the public folder might or might not be located in or have a replica in the same routing group as the user ‚ s Exchange mailbox. In addition, in any routing group there will likely be more than one public folder store. These factors combine to cause a public folder referral to be necessary to allow clients to successfully connect to the desired public folder. Two different, but related , scenarios exist with public folder referrals: one in which the public folder or a replica does exist within the same routing group as the user ‚ s mailbox and one in which the public folder or a replica does not exist within the same routing group as the user ‚ s mailbox.

When a user attempts to connect to any public folder, the connection is first attempted on the public folder store that is configured as the default public folder store for the mailbox store that houses their Exchange mailbox. If this public folder store does not contain the public folder in question or a replica of it, then the client will connect randomly to another public folder store in the same routing group. This process will continue until the desired public folder or its replica has been located or until all the public folder stores have been exhausted within the routing group. When this happens, a public folder referral must occur in order for the user to successfully connect to the desired public folder.

Although we will examine this in much more detail in Chapter 8, ‚“Building Administrative and Routing Groups, ‚½ we ‚ ll briefly mention here that routing groups are connected to each other using routing group connectors. Routing group connectors, much like a link between two routers, have a cost value associated with them. The cost value can range from a low value of 1 to a high value of 100, with lower values indicating the more preferred routes out of the routing group. When a client needs to connect to a remote routing group (for any reason, including public folder referral), the routing group connector that has the lowest cost value will be used if the routing group connector is configured to allow public folder referrals across it (see Figure 6.14). By default, all routing group connectors are configured to allow public folder referrals; however, this can be disabled by selecting the Do Not Allow Public Folder Referrals option. If a routing group connector allows public folder referrals across it, then the client will continue the process of attempting to locate the public folder or a replica of it in any routing group to which it can connect.

Figure 6.14: Allowing public folder referrals across a routing group connector

As an alternative to allowing ‚“random ‚½ public folder referral, you can configure servers that contain public folder stores with a predefined list of referrals, thus forcing clients to use the configured list. The Public Folder Referrals tab of the server Properties dialog box, seen in Figure 6.15, allows you to change the default option of Use Routing Groups to Use Custom List. When you select the Use Custom List option, you can then configure specific servers and the cost values that are to be used for public folder referrals.

Figure 6.15: Configuring a custom referral list