From now on you may create your emails including a tablet version in Responsive.email Studio. So all together you can have two mobile versions which get active at your defined breakpoints (e.g. upto 480px screen width the smartphone version, from 481px to 640px the tablet version).
Additionally there is a new attribute "stack for". With this you can control if responsive elements (Responsive Stack / Responsive Reverse) should stack already at the tablet or only at the smartphone version. Like before, with the (in)visibility property elements can be shown or hidden exactly for certain views.
The mobile versions will get active automatically in the supported clients. Supported are e.g. the native Android app and the iPhone / iPad, but not the Gmail App. Unfortunatly the Gmail App has no support for media queries.