Microsoft Outlook not staying set as default mail application?

Microsoft Outlook 2016 Icon

Need to set Microsoft Outlook 2015 as your default application on Mac OS X Yosemite or El Capitan?

Using the preferences from doesn’t save Outlook as the ‘Default email reader’…

A solution is to open Mail, and on the general tab, instead of using the drop down menu to select Outlook, Click on Select and browse to the Applications folder and select Microsoft Outlook.