That was a pain but here's the question: How did they (advertisers) know this box was open and active? If mail was going to it before I opened it, what did they do with it? I tried complaining but got the "we have to deliver every piece of mail regardless of the originator". My best guess is mail was being sent there from a previous user and while it was vacated they just threw it away or something. Once the new user (me) opened it back up I just started getting it all.
At one point I just let the junk accumulate to see what would happen. I'd get the "real" mail but the junk (which could no longer really fit) stopped showing up. Then I got a note that I need to clear it out more often or they would close it though :(