Just remember to tear-off anything that looks personally identifiable ( address, reference numbers etc ).
There used to be a trick in the UK of attaching reply envelopes to bricks and putting them back into the postal system, hoping that the spammer would be charged by weight, but Royal Mail put an end to that.
Slightly OT but that's because one of the biggest customers of postal services are direct marketers. By sending a brick you're abusing the system and harassing the real customers.
