This is an accepted solution.
you can add newsletter
Refer this link it has guidline to add newsletter
From your Shopify admin, go to Online Store > Themes.
Find the theme that you want to edit, and then click Customize.
Click Add section.
Click Newsletter, then click Add.
Enter a heading for your newsletter signup. For example, "Subscribe to our newsletter".
In the subheading field, enter a short description of what your customer will receive by subscribing.