I agree with the importance of working email client.
Actually, I would like to try Ubuntu Touch, and the lack of tolerable email client stops me.
I think dekko is getting close to being usable on xenial, just a matter of fixing a couple of bugs still lingering with the build. It already works great using the current stable 15.04 (vivid) release so you can take that for a spin.
By the way, its curious what would cost to adopt https://sailfishos.org/wiki/Email? Can we run their programs easily?
I believe the email app like others are not open source by Jolla. Just the framework referenced above which dekko I believe is already using. Also given that Silica is also proprietary it like other Sailfish apps would have to be modified in order to work properly.