Pre Paid return envelopes question.

[haaammit]

The ones that you get from banks/businesses/junk mail etc - how do the companies get charged? I can only assume they only get charged if the envelope is used, if not it would cost a fortune!

Do Royal Mail send an invoice for each one? Is there a cost/size limit? We occasionally get junk mail with pre-paid return envelopes and I was wondering what would happen if I wrapped up a brick and used the return envelope thingy to send it - would the company get charged the whole postage amount or would they get one of those 'the sender didn't pay enough postage so collect from the post office' type letters through?

I've often wondered.

Quink

 

[haaammit]

So basically any junk mail you get post them back their empty envelope just to be a tool?

Why is it being a tool? It's unwanted mail. Why shouldn't I cost those companies money? I didn't ask for the rubbish to be delivered to me.