We are using Webmail Enterprise Edition Version: 16.3.6628, and if you try to save an RBL entry that does not have a Required Lookup Values (even with this option turned off) it will not allow you to save the entry. The Save button is enabled, but clicking it does nothing. In order to save, you need to enable the Required Lookup Values and enter a value, and then disable the Required Lookup Values option. It seems as if even with the option disabled it is still doing server side validation of this field and returns the response -

 

{"message":"LookupResultsIndicatingSpam must be IP addresses"}