Free envelopes with postage in exchange for watching ads by email

A new trend report on consumers being able to order envelopes with free postage mailing within The Netherlands, as reported by Springwise. There are two conditions though: there are advertisements printed on the back of five free envelopes per week and consumers must agree to receive ads by email for four weeks. My first thought to this was that not many consumers would go for it, but Gratis-Post actually ran out of envelopes in the first week, with 52,500 envelopes going in just a few hours after launch.