[kingcanuteus]

If it is a return envelop, return it empty. Let them pay for the postage.

[Big Horn]

I stuff it with papers.

[Mr. Lucky]

I always cram all of the contents of their original envelope into the return envelope. That way, they not only have to pay extra postage, but they naturally assume they have some senile old fart on the hook (which they may have) and immediately send me more stuff. It's pretty close to a perpetual motion machine.

[dangerdoc]

I would recommend stuffing it full of your other junk mail and letting them pay for the extra weight.

[Anti-Bubba182]

Tape pennies to a card. They pay by weight.!