Can SharePoint objects like 'SP.ClientContext' be used while developing Office 365 Mail Addin?

I am developing a Office 365 Mail Addin in Napa. I am trying to use the object of SP.ClientContext but it shows me error that SP is not defined.

Office.initialize = function (reason) {
    $(document).ready(function () {
        app.initialize();

        var context = new SP.ClientContext("https://mysite.sharepoint.com/"); // <-- Error
        var web = context.get_web();
    });
};

I would like to know can SharePoint objects like SP.ClientContext, SP.Web, etc. be used while developing Office 365 Mail Addin? If yes, then what is the best approach for the same?