As a legacy version, 5.6.3 has developed several significant maintenance challenges for those still running it:
(Caching Server, File Sharing, Time Machine Server) macOS Server 5.6.3
Does 5.6.3 delete deprecated services? - Apple Support Community As a legacy version, 5
for new installs; fully functional for existing upgrades. Management Tools (Profile Manager, Open Directory, Xsan) Active and supported as the primary focus. As a legacy version