One way or another you would have to build a custom project for that purpose, either building on customizing the SD.Email.Monitor or a completely custom project.
The project in Bulk Closure article is for the purpose of always making the tickets closed, forcefully, if needed. I would not recommend to use the same approach for tickets that are functional and for the use case of closing with e-mail that I assume would become fairly normal procedure.
The 'good' way to do this is with 'Send Complete Workflow Message' component that is able to send a message to the Work Incident task to pick up.
Using this is straightforward enough only in specific circumstances. Namely, you can close get incidents in 'Work Incident' stage - with the functional 'Work Incident' task. You cannot do the same with Incidents in other stages/tasks like on Hold or in Confirmation. Any other stages, additional tasks etc will pose a serious problem as Alex can probably attest to.
However, doing this does require understanding how processes and tasks work and good ability to build Workflow projects and integrate these into ServiceDesk. What I am trying to say is you would have to do serious testing messing with process by external means.