WordPress.org

You can either install it automatically from the WordPress admin, or do it manually:

1. Upload the whole wp-email directory into your plugins folder(/wp-content/plugins/)
2. Activate the plugin through the 'Plugins' menu in WordPress

Once installed take the following steps to set it up:

1. Under E-Mail Settings, modify the setting Method Used To Send E-Mail accordingly. If the method is wrong, no email will get sent.
2. You Need To Re-Generate The Permalink (WP-Admin -> Settings -> Permalinks -> Save Changes)
3. Refer To Usage For Further Instructions

Usage

1. Open wp-content/themes/<YOUR THEME NAME>/index.php You may place it in single.php, post.php, page.php, etc also.
2. Find: <?php while (have_posts()) : the_post(); ?>
3. Add Anywhere Below It: <?php if(function_exists('wp_email')) { email_link(); } ?>

If you DO NOT want the email link to appear in every post/page, DO NOT use the code above. Just use the shortcode by typing [email_link] into the selected post/page content and it will embed the email link into that post/page only.