How to ensure legitimacy when renting a property over the internet?

Hi i need to rent an apartment or room in Copenhagen for when I move there in September.I have been in contact with a few landlords mainly through the expatriates.com website but I am very wary about handing over any deposit or initial rent but on the other hand I can't make it to Copenhagen before I start studying so something needs to be done.I was Just wondering if people knew any ways to ensure a landlord is legitimate or ways of agreeing a deal without sending any/much money.Thank you.