Maintenance (Speed Up Mail) issue

When I open my CleanMyMac 3 application and go to maintenance, I attempt to use the "speed up mail" feature. However, when I go to click the little box that tells the application that I want to run it, it shows a little i with the message," your mail application is not set up. task not available." any ideas as to why this is happening and how i can fix it?

Welcome to our forums.

The first thing we advise you to do is get rid of CleanMyMac 3. The program is supposed to be benign but has been known to be overzealous in removing items and claiming to be able to speed things up. Also, it would help us to help you if you tell us which Mac you have (year and model) and what version of OS X it's running.