He would have had better luck cutting letters out of a newspaper, sticking them to a page and popping it in the post. However that is not without its hazards.

He would have had better luck cutting letters out of a newspaper, sticking them to a page and popping it in the post. However that is not without its hazards. He would need to evade CCTV and make sure he did not take his cell phone with him to the post box. The stationary he used would also have to be untraceable, so a stack of identical envelopes at home would not be ideal. He would also need an alibi lest any neighbours end up why he was posting letters at 4 a.m.