Returns true if this Folder has new messages since the last time this indication was reset. When this indication is set or reset depends on the Folder implementation (and in the case of IMAP, depends on the server). This method can be used to implement a lightweight "check for new mail" operation on a Folder without opening it. (For example, a thread that monitors a mailbox and flags when it has new mail.) This method should indicate whether any messages in the Folder have the RECENT flag set.