Security with qmail-hashdir
                  ===========================
'Out of the box', I've tried to avoid any obvious security pitfalls. In
particular you'll notice that the Makefile creates all its binaries and
scripts as readable and executable by the alias (or nominated hashuser)
user. Depending on your configuration, you may wish to modify this:

 - The showhashdir may prove to be a useful tool that you'd like to be
   able to run as other users. This can be enabled by giving read/execute
   permission to a group and/or 'other' for this binary.
 - You may wish to be able to run the various addhashuser etc. binaries
   when logged in as a different user. This can be accomplished by
   opening up the rights on these files, and setting chhashdir,
   addhashuser and addhashalias to be SetUID alias (or hashuser). This
   could offer a security breach however, enabling any user to execute
   arbitrary commands as the hash user. I would only
   recommend this if you have multiple machines backing onto a shared
   NFS device - in which case, only open up the rights on a machine that
   has no Internet connectivity - a machine attached to a private
   network only (which would also be where the NFS device is located).
   Also beware of mount options that may affect whether SetUID can be
   used anyway.