We are really not happy with current state of the Email App, because it suffers a lot of small malfunctions, and its foundations aren't strong enough. Instead of trying to apply patches to fix the issues one after the other, we decided a few months ago to perform a pretty big refactoring, to clean up the code and build stronger foundations. During this refactoring, we have disabled some features, for example message composition, that had a really strange, random, issue.
Unfortunately, our priorities have evolved, and we had to put this refactoring to sleep. For now, we are working on improving the performances of the core of the platform. You can find our updated roadmap for 2017 in this article: https://blog.cozycloud.cc/post/2016/11/21/On-the-road-to-Cozy-version-3
The future of the Email application is pretty uncertain for now. We won’t work on it until this summer, and should then decide if we finish the refactoring or give up and try to port another webmail to Cozy.
Until then the application will be removed from our application store, as it is not really usable.
I’m really sorry for the annoyance. I hope our other applications will better fit your needs.