IMAP and IMAP clients permit so-called hierarchical folders. The forward slash character, / , is used as the hierarchy separator, just as when specifying subdirectories and files. And indeed, for the native Berkeley mailbox, hierarchical folders are implemented as UNIX directories and files. That is, for the native Berkeley mailbox an IMAP hierarchical folder /apple/banana/carrot will correspond to the file carrot within a subdirectory /apple/banana/ under your default directory. Note that hierarchical folders in PMDF MessageStore mailboxes do not correspond to UNIX subdirectories in this way.

It is not necessary to create "intermediate" folders before creating a terminal folder; for instance, folder /apple/banana/carrot may be created even if the folder (which in the case of a native Berkeley mailbox is implemented as a subdirectory) /apple/banana/ did not previously exist; the IMAP server will create the necessary folder (the necessary subdirectory in the case of a native Berkeley mailbox) for you automatically.

Note that since "intermediate" folders for the native Berkeley mailbox are actually UNIX subdirectories, it is not possible to store messages in such "intermediate" folders; messages may only be stored in a file at the "end" of a folder specification. But with PMDF MessageStore mailbox hierarchical folders, as they are not limited by subdirectory issues, it is possible to store messages in "intermediate" folders.