Basically repeating what I answered for another question, I'm all for rolling-your-own in most situations, but when it comes to mail I'd heartily recommend making it easier on yourself and using something like Swift Mailer or PHPMailer (in that order, for my money).
As a side-bonus (and assuming you specify reply-to, etc), you also have much less chance of being tagged as spam.
EDIT: Maybe it's just the example you've used, but there's no actual HTML in your message. Why not just use plain text? And yes, I'd use one of the classes I suggest for plain text too.