This app shows you how to set up an email contact form for your website. The form takes an email address, a subject, and content and builds an email that is sent via the SendGrid API.
Note that you can't use the submitted email as the from address, to send with SendGrid you must use a verified sender or, preferably, an email from an authenticated domain. In this application the user submitted email is set as the "reply to" email, so that when you reply in your email client, it will be addressed to the user.