Create new transactional email template
- Go to: Magento admin panel >> Marketing >> Email Templates >> Create New with MTEditor.
- Choose email template, store and locale
- Enter template name and press the button "Create new"
Now you have to apply this template in system configuration. For example if you have created "Newsletter subscription success" email template you have to go Magento admin panel >> Stores >> Configuration >> Customers >> Newsletter >> Subscription options >> Success email template and choose before created template.
That's all. You are ready to go!