How to send html and text email via JMail Joomla! 3 api

How to send both version html and text with JMail Api in Joomla! 3

We can only send html only or text only by default with Joomla! 3 's JMail API.
But with this tip, from now on you can send both html and text email versions at once.
Kind of useful to have a better score and try not to be in mail clients spams. Here is the code