Using Mail Body Initializer templates
Mail Body Initializer templates is a concept to initialize the Body field in the Email Screen when you want to send emails manually. Contexts can define a single Mail Body Initializer template. For more information, see here.
These templates are regular email templates that you can develop in Jira Email This Issue, however you must understand how they work in conjunction with the templates you use to render the final email.

How Mail Body Initializer templates work

Mail Body Initializer templates can be composed by using HTML, velocity. They may contain issue fields, regular text and many more.
When you open the Email screen, the Context related to the current issue is determined. If the Context is configured with a Mail Body Initializer template, the template is evaluated and the result is set in the Body field.
It is a good practice to add a distinguishable template category name for these templates so that they can be easily identified.

Templates to send emails prepared with Mail Body Initializer templates

Contexts have an Email Template attribute. This specifies the template used to send the emails sent manually.
Important: If you configure the Context with a Mail Body Initializer template, do not to use the same template for Email Templates and Mail Body Initializer templates, nor should you have overlapping content, otherwise content will be duplicated in the email as the Body field is added to the template via the variable $!mailBody.
Instead, if you have a Mail Body Initializer template, we recommend you create a template as simple as $!mailBody and select it in the Context's Email Template field.
Note: Mail Body Initializer is only applicable to emails composed manually. Event Notifications or Workflow Post functions should be configured with regular, detailed templates.
For more information, see the sections Event Notifications and Workflow Post Functions.