IMAP Access to Public Folders

When a non referral-enabled IMAP client connects to a back-end server, it can access only public folders that have a replica on the user's home server. To access public folders that have replicas on other servers, an IMAP client must be referral-enabled. A referral-enabled client issues special commands to an IMAP server to create a list of the public folders available to the client. When the client computer requests a public folder that does not have a local replica, the server responds to the client request with a referral URL that contains the name of the server that has the public folder. The referral-enabled IMAP client computer then creates a new connection to that server to retrieve the appropriate information.
In a front-end and back-end topology, however, the front-end server acts as a referral-enabled client, so IMAP clients connecting to the front-end server do not need to support referrals; the front-end server handles referrals for them. It transparently maps non referral-enabled client requests to their referral counterparts, making the entire list of public folders available to a non referral-enabled client. When the front-end server receives a referral response from the back-end server, it does not pass this response back to the client. Instead it follows the referral for the client and makes a connection to the appropriate back-end server that has the data. The back-end server then responds with the requested item, which the front-end server relays back to the client.