The IMAP4 server options provide a means of creating a public mailbox in which you can post messages for reading by IMAP4 clients. To create a public mailbox, create a user ID named "public". Any mailboxes in this user's directory will be available for reading by IMAP4 clients.
Administrators can use the public user ID to post messages. Users other than public can only read the public mailboxes. Administrators can set an option that determines whether users must subscribe to a public mailbox before they can read it.
Public mailboxes are read-only by design, and only the user public can administer the public mailboxes. Messages received for this account and its sub-mailboxes are treated as normal, but users other than public who access these mailboxes through IMAP4 have read-only permissions. If a user tries to mark a message in a public folder as read, he will be notified that the mailbox is read-only.
Note: Subscribing to a mailbox is a protocol-command; there is no way for a user to subscribe to a mailbox unless the client application provides this capability.