In order to perform send mail action in a project by using already created Mail Task's created template, please follow the below steps:
1) Open any incident in a project where you have your project mail template created (i.e. see below)
2) You will be presented with similar prompt as the one below:
present elements are:
Template - please select the one from the drop-down menu list;
Create New Template button - you will be redirected to this screen to create a new project mail template;
(to be continued)