Jetpack has an answer for this. This is for self hosted WordPress.
First, open your functions.php inside wp-content/themes/your-theme/. Add the following line:
add_filter( 'jetpack_allow_per_post_subscriptions', '__return_true' );
You are done!
Every time you want to post a new post, you will see a checkbox. Tick, if you don’t want to email your subscribers of your new post.