Schengen

As is the case for the other Member States participating in Schengen, Greece issues, on the one hand, Schengen uniform visas, and on the other, national long-stay visas for stays exceeding three months.

One of the requirements in Schengen, quite practically, is that you have configure airports so that you can separate out your air travellers from those who are travelling within Schengen and those who are not.