Launching the mail app from a WIndows Store app

I'm trying to create a windows store app that will launch the default mail app (WinJS 8.1). I haven't touched this for a while, but it was working correctly before 8 - 8.1 upgrade. The code looks like this:

var interval = setInterval(function () {
    clearInterval(interval);
    var formattedBodyText = bodyText.replace(/\n/g, '%0d');
    var mailTask = Email.SendNewMail.sendEmail(emailAddress, subject, formattedBodyText);    
}, 500);

And the sendEmail function:

sendEmail: function sendEmail(addess, subject, body) {
    var mailto = new Windows.Foundation.Uri("mailto:?to=" + addess + "&subject=" + subject + "&body=" + body);
    return Windows.System.Launcher.launchUriAsync(mailto);
}

Oddly, this seems to launch Chrome (I assume because that's my default browser). How can I get it to launch the mail app? Has this changed since the 8.1 upgrade?

EDIT:

It looks like the default program for opening mails was changed to Chrome. So, I suppose my question is now: is it possible to FORCE the mail app to open, rather than whatever is associated with the mailto: url? I noticed there was an ms-mail uri - would that be safer to use?