Check out the full comparison between YayMail Free and Pro so that you will have an informed decision. Maybe a YayMail Addon is your missing piece!
Both YayMail Free and Pro provide the core functionality of editing email content and customizing email designs. You should upgrade to Pro if you want to display variables and placeholders from third-party extensions in the emails.
Please note that YayMail Pro does not include third-party email templates.
If you are using a third-party WooCommerce extension that adds new email templates to the 11 default email notifications, you can buy a dedicated YayMail Premium Addon to customize those emails.
YayMail Addons can be bought apiece and added to your current YayMail core. A YayMail Addon works with either YayMail free or pro version. From then on you can edit all the newly generated email templates in YayMail's drag and drop framework.
Here's the complete list of plugins that generate new email templates which can be fully customized by YayMail Addon: