When I use this formula 

=HYPERLINK("mailto:"&B4&"?subject=“& B5 & “&body=“ & B6,", "test")

in the excel, I am able to click on the link which opens up my mail client with compose new email window and also populates To, Subject and Body of the email from cells B4, B5, B6 respectively.

But currently, HYPERLINK formula does not support "mailto:" functionality in Kendo UI spreadsheet. I would love to see this with kendo UI spreadsheet. 

For more details you can see the discussion on the forums here.