I had a client that was looking to automate uninstalling/reinstall rightfax client, and needed to delete the registry keys created by rightfax after the automatic uninstall took place.  Faxutil generates registry keys in two hives as follows:

HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Rightfax Client

HKEY_CURRENT_USER\Software\Rightfax Client

 **NOTE: For 32 bit clients, remove the Wow6432Node folder.**

Since it was automated, he did not have access to the Current User registry, but removing the HKLM keys seemed to do the trick for his process.  Once these keys were also deleted, he was able to perform the uninstall/reinstall.