How can I stop my sent emails from containing raw HTML? When I send an email from my official exchange server, the person who receives it, whether through web access or through Outlook, gets the email with HTML coding! It is very embarrassing and I have searched for the solution in vain. How can I stop this behavior?
Making text encoding the default behaviour for the stock Android Email app is not possible. You can use K9mail instead. This question is already answered here. 

https://android.stackexchange.com/questions/9237/disable-html-emails-in-composer