Although an email address is just text it is useful for the browser to know it is an email so it can treat it differently.  Add this code just before the submit button:

    <label for="emailaddress">Your email address: </label>
    <input type="email" name="emailaddress" id="emailaddress">

Try the page and if you enter an email address it should work.  Enter something which is clearly not an email address and it should be rejected when you try to submit the form.

You can also tell the browser whether to remember the email address and automatically put it in next time (useful for logging in).  If you want to have the browser remember the user's email address you amend the code to this:

<input type="email" name="emailaddress" id="emailaddress" autocomplete="on">

Once you start typing the email address a second time it should offer the finished address.