Can letters of recommendation be sent after application deadline in Politecnico di Milano?
You should double-check the application instructions and if nothing is there, then call the admissions officer in the school. My guess is that there is not a problem, but it is better to be safe.

Often, this is not an issue. Referees are contacted via email by the university and they submit their applications themselves electronically, either by following a link or by email. The requirement for the application is usually limited to name the referees, not submit the references themselves. These days, it is uncommon for "sealed, stamped and signed" references in paper to be submitted, and including open references in applications is also not usual (although I have done so personally). I know it happens, though, but all in all reference submissions are often not bound by the same deadlines as the applications.