Can I have subfolders not appear under INBOX?

The altnamespace setting in /etc/imapd.conf changes the way the mailbox list is presented to users (including fileinto directives in Sieve scripts). Instead of appearing as subfolders of INBOX, altnamespace makes subfolders appear at the same level as INBOX. It does not affect the internal storage nor the way the folders are presented through cyradm. See imapd.conf(5) for more information.