I am sorry to be this guy, but this seems similar to what http://avivaiq.com does as a product, for free (for the time being at least).
However, in my experience, Airbnb customer service doesn't keep a log of emails exchanged between guests and hosts (although they are processed under their proxy). So if a guest complains because they have not received that email, Airbnb will systematically side with the guest if they complain.
Anyway: nice to welcome you on Smartbnb! We don't send messages over email for this limitation, but we do send native Airbnb messages.