For every project, the ARN page has a tab called 'Logs'. This page displays entry of all execution logs. Any time a rule is executed, irrespective of its trigger or template - corresponding entry will be created in the logs.
Along with all the related details, these logs also have a link 'View email'. Clicking on this link opens the email that was generated by the rule.
Logs are helpful in keeping track of all instances when the rules were executed.