Vatfree.com
Is there a vatfree.com mailbox at the airport? /

To submit your request at the airport, please deposit your envelope with receipts in a mailbox of the national postal service.

All airports have a general postal office or mailboxes of the national postal service in various locations. To be sure, check the airport website or contact customer services a day before your departure. You can also ask an airport employee to point you in the right direction.

At Schiphol, Amsterdam airport you can use the orange mailboxes. There is an orange mailbox  located across the hall from customs. 

Don't forget to use an envelope, a postal stamp, your contact details and registration numbers.