window.open('mailto:firstname.lastname@example.org') is inconsistent among platforms. On iOS it opens native email app, on Android and WP it silently fails and do nothing.
On the other hand window.open('tel:650-349-9067') works on Android and iOS but not on WP.
I know now that one can add second parameter _system to window.open to enforce opening link in native browser but the main problem is that it is not evident for the first look. It took me two hours on my project to find out that it is the InAppBrowser plugin which causes that my email links don't work on Android while it works on iOS.
I suggest we fix mailto: links opening on Android and WP to make it consistent and I'm able to provide pull request for this.