Works here on 2015.12 and OS X 10.11.6
Have you checked the crash log error? Please share the crash log error with us.
I'm having the same problem here on my laptop with a new Windows 10 installation.
As soon as I click anywhere on the dialog Lightroom goes 'non-responsive'. This is driving me nuts as I want to email photos directly from LR.
I have tried switching off the graphics option in Preferences and have also reset preferences but nothing seems to work.
Any help would be appreciated.
What is your exact (numbers, not latest) version of LR?
What is your OS and how are you trying to email (gmail, local email client ..)?
Lightroom Classic version: 7.0.1 [ 1142117 ]
Operating system: Windows 10
Application architecture: x64
System architecture: x64
Graphics Processor Info:
OpenGL: GeForce GT 540M/PCIe/SSE2
Check OpenGL support: Passed
Vendor: NVIDIA Corporation
Version: 3.3.0 NVIDIA 359.46
Renderer: GeForce GT 540M/PCIe/SSE2
LanguageVersion: 3.30 NVIDIA via Cg compiler
Total Video Memory: 1024 MB
I will use gmail if I can get this working on my laptop. All works ok from my desktop.