many of you guys may have done the mailbox thing and gotten away with it, but take it from me personally...
delivering fliers for my uncles fert. company, put over 500 on mailboxes, not in, but between flag and box. he got a $385 fine.
second time, my business fliers, put them on mailboxes in a different town, different post office and all that, the post lady picked up everyone of them, didnt turn them in, but called me personally and said dont do this crap anymore.
theres your living proof. it is illegal, cops dont have anything to do with the mail. just dont it, not worth a fine.