John McCain is not reachable by traditional email, as of 2015. Instead, contact him by using the Contact Form available on his official Senate website. Fill out the form using your first and last names, address and other requested information.
Select a subject for your message from the drop-down mandatory subject line on the Contact Form. It lists various message topics, such as agriculture, the second amendment, taxes, veterans affairs and defense. Below the subject selection box is a message text box for leaving a personalized message. The end of the contact form also includes a selection to indicate whether or not you wish for the senator to send a response.