Email template
Pick a template from the drop-down to use for the email. The HTML/text body will appear inside that template.
Blank/Basic
With the Basic/Blank template, the email received will not have issue information and links to the issue key, unlike the Default Jira Notification Email template.
Default Jira notification template
With the Default Jira Notification template, the email received will have information and links to the issue key as shown below.
No template
There will be no formatting to the Email sent when you select No template