: mailbox
      The mailbox with the associated quota.

: mailbox
      The mailbox with the associated quota.

: mailbox
      Returns the mailbox name.

: mailbox
      nil indicates end of imap.rb"/[RFC-822] group.
      If non-nil and host is nil, returns imap.rb"/[RFC-822] group name.
      Otherwise, returns imap.rb"/[RFC-822] local-part

