To see this button at the bottom of your content (pages, blog posts, photos, etc.) go to Settings > Global settings> Plugins
and check the Enable social sharing box. Select the "Email" service.
You can choose the display style, in the form of icons or buttons of different sizes (with or without sharing counter).
As with all plugins on the site, this option is managed at 4 levels. It is possible to display this option for the whole site or only on a specific add-on, a category or an add-on element (a specific page of your website for example).