Greymail Inboxer is an augmented reality game for Android, iPhone and Windows Phone that involves users catching and sorting virtual emails that fall from the sky all around them.
The free app requires quick reactions and good spatial awareness to score maximum points, as missing too many items means game over.
Greymail is a term used to describe the legitimate but 'mostly unwanted' messages that clog up email inboxes, such as newsletters, social network updates and special offers.
Microsoft said that skilled players in the game will learn how to "conquer their greymail backlog with ease", using the 'Sweep, 'Schedule Cleanup' and 'Flag' features of Hotmail to sort their virtual inbox.
Users can progress from being a "featherweight inboxer" to a "heavyweight", gaining badges as they progress and moving up the leaderboards.
The 'Greymail Inboxer' app is available now to download for Microsoft's Windows Phone, Apple iPhone and Google Android.