Hi,
This is a modified version of Application Open Url, so that it will only generate a mailto link, with the option to add a Subject and Body text. 
It will get rid of the formatting problems that sometimes happen when adding text to fields in Application.OpenURL
I tested only on iOS and the editor, but it should work in any platform where Application.OpenURL is supported.
// (c) Copyright HutongGames, LLC 2010-2014. All rights reserved.
using UnityEngine;
namespace HutongGames.PlayMaker.Actions
{
	[ActionCategory(ActionCategory.Application)]
	[Tooltip("Open a Mailto Url link in the browser or email client")]
	public class ApplicationOpenUrlMailto : FsmStateAction
	{
		[Tooltip("Email Address")]
		public FsmString inputEmail;
		[Tooltip("Subject")]
		public FsmString inputSubject;
		[Tooltip("Body")]
		public FsmString inputBody;
		public override void OnEnter()
		{
			string email = inputEmail.Value;
			string theSubject = inputSubject.Value;
			string theBody = inputBody.Value;
			string subject = MyEscapeURL(theSubject);
			string body = MyEscapeURL(theBody);
			Application.OpenURL("mailto:" + email + "?subject=" + subject + "&body=" + body);
			Finish();
		}
		string MyEscapeURL (string url)
		{
			return WWW.EscapeURL(url).Replace("+","%20");
		}
	}
}
I hope someone else finds it useful.
Cheers