Officially the ThinkPad Mini Dock Series 3 (model 4337) only supports 2 screens (either two external or one external plus laptop), but this is me running 3 screens (2 external plus laptop) only connected with the DVI and Displayport form the dock. The laptop is a ThinkPad T430 with the integrated Intel 4000 graphics. The system is Debian stable (Jessie) running XFCE (with Compton compositor).
What I'm writing is the execution of a small xrandr script for quickly switching between 1 screen (laptop), 2 screens (both external) and 3 screens (laptop plus 2 external).