Thanks for a bug report. I'm not able to run Wayland in Fedora 21 at all (I have it offered, but the virtual machine doesn't run properly after I enter my password, the desktop is only all grey and nothing can be done). Anyway, the message list is a custom widget, which does some drag&drop, certain parts on its own, but it used to work. Could you try a more simple application, like for example the gtk3-demo, its Icon View->Editing and Drag-and-Drop example, whether it'll work, please? I guess it will, but just in case.

Sorry for the delay, I had to stop using the Wayland session for a while due to unmanageable issues. I've just tried out gtk3-demo as requested, and it does not work the same between X and Wayland sessions. 

The behavior here though it even different from what I see in Evolution. In Evolution, I can pick up the messages to initiate a drag, but I can't drop them in a folder. In gtk3-demo, I can't even pick up the icons to drag them around.

Thanks for testing this. I would start with the gtk3-demo and if their fixes will not correct evolution, then continue with it afterwards. Could you provide your gtk3 version, please?

I just tried, and both the gtk3-demo drag demo and evolution message dnd work here now.