How do i open a mail launcher in Metro app (WinRT 8.1+ ) - Xamarin.Forms

I am trying to send mail using launcher in PCL WinRT app. Launcher works proper for normal mail, but if i try to send mail with HTML body, it fails to launch.

Launching mail pop-up using :

string mailtoUri = string.Format("mailto:{0}?subject={1}&body={2}", toEmail, mailSubject, bodyText);
Launcher.LaunchUriAsync(new Uri(mailtoUri, UriKind.Absolute));

Fails when
bodyText = html head /head body > some mail text </body /html>;

Thanks in advance.