If they persist then just stuff carboard etc in the envelope as well. This becomes overweight mail and so they have to pay royal mail a surcharge on delivery. That one never fails to get them to stop sending you stuff :)

I have yet to resort to posting anything as big as an old tyre :)

Returning junk mail to direct mailers on their dime (by stuffing it back into their postage-paid return envelopes) may cost them some money and provide you with a bit of personal satisfaction, but it won’t cut down on the amount of junk mail you receive. In fact, it may actually increase your junk mail load, since the primary metric used to gauge the effectiveness of many direct mail campaigns is the number of responses received (even if those responses are negative). The best way to decrease the amount of unsolicited mail you receive is to register with the Direct Marketing Association’s (DMA) Mail Preference Service (MPS). The DMA maintains a “do not mail” file of MPS registrants which they regularly update and send to their members, who are required to remove the listed entries from their rosters of prospective customers targeted for mailings. (The file is also made available to non-DMA members, but they are under no obligation to use it.)

As for the rules, The Straight Dope has the dope that is straight:

Unfortunately, your bricks-for-business scheme, admirable though it is in theory, won’t work in practice. According to rule 917.243(b) in the Domestic Mail Manual, when a business reply card is “improperly used as a label”–e.g., when it’s affixed to a brick–the item so labeled may be treated as “waste.” That means the post office can heave it into the trash without further ado.

Once upon a time, they tell me, things were different. Years ago, it seems, postal regulations required that all business reply mail be delivered, whether the cards were affixed to bricks, 2x4s, or hand grenades. Furthermore, the recipient was required to pay full first-class postage (a good buck, in the case of a brick) plus 18 cents handling per piece. However, the direct-mail firms usually worked out a deal with the local postmaster whereby unwanted building materials and whatnot (believe it or not, Win, you’re not the first person to think of this) somehow became “lost” (heh-heh), getting the mailing firm off the hook.

The current regulation makes it unnecessary to resort to this subterfuge. But most people don’t realize the mailing firms won’t get stuck with the tab, so a fair amount of oddball junk still finds its way into the nation’s mailboxes. The postal service regards this as a major pain in the neck, and therefore I have been implored to convey to the Teeming Millions the following message: putting bricks in the mail could bring American civilization to its knees. (That’s the impression I came away with, anyway.) Also you might be charged with “abuse of the mails.”

Marilyn Vos Savant was not available for comment.