Service Desk Mail Handler: Create a way to disable comments from email vs creating issues from email and vice versa

Problem description

When configuring a Service Desk Mail Handler in Project Settings > Email Requests, there is no setting that allows us to decide whether we want to use the mail handler to:

1. both create new issues and add comments to existing issues
2. only create new issues
3. only add comments to existing issues

As of now, only the 1st option is available.

This is a problem for customers who want to use the Mail Handler to only create new issues, or only add comments to existing tickets. As a result, some customers decided to use the JIRA Core Mail Handler configured in ⚙ > System > Incoming Mail, since this mail handler is more customizable.

That mail handler is unfortunately not a proper mail handler to use with Service Desk projects, since it was originally designed for JIRA users (users with a JIRA license) and not for customers (users without a license). Therefore, when using the JIRA Core Mail Handler, it is necessary to provide as many licenses as customers (while the Service Desk Mail Handler does not require any license for customers).

Suggested solution

Make the Service Desk handler more customizable, so that we can configure it to either add comments, create new issues, or perform both actions.