Follow

How to Change Default RSS Reader on macOS

If you are using macOS Mountain Lion or later, note that Apple removed the RSS preferences from Safari, leaving users with no way to set a default RSS reader.

Many customers have had success in using the following 3rd party application (however, we have not tested this extensively at Postbox): 

http://www.rubicode.com/Software/RCDefaultApp/

 

For more information, please search Google for "Default RSS macOS"