I've recently been receiving lots, and lots, and lots of junk mail. I was discussing this with a friend, who knows someone who collects all theres and does something rather amusing with it.
I now save all my junk mail

I put the contents of one- into the pre-paid envelope of another and post

. In 2 days I've sent 4 letters back...passes the time !
Do your bit, they might think twice about sending cr@p out then ?¿