For each entity type, you can determine a default template. This template will be the template automatically used when clicking the Email icon for the entity (without choosing a template from the list with the arrow).
To set a template as the Default Email Template, right-click the template in the list, and select the Set as Default option.
Set a Default Email Template
After setting an Email Template as default, it will show the Default indication in the templates list.
Only one template of each type can be the default template at a certain time, so setting a template as default will switch an existing default template.