Currently if you have two mail handlers which conflict, you can't choose which mail handler you want to run first. For example:

1. First Mail handler is for "Add a comment with the entire email body", which applies to ALL projects
2. Second Mail handler is for "Create a new issue from each email message" for ABC project
3. Send an email with the subject "Test ABC-1" (assume ABC-1 is an issue which exists already)
4. Expectation is a new issue gets created, however, ABC-1 gets a new comment.