Question: How many sheets of paper can you put in an envelope before you need another stamp? 

Answer: one ounce worth, but if it is too bulky they will send it thru the spurs, bulky material that cannot go thru the machine, and the person on the other end will have to pick up the postage due. I'd say that if you have trouble folding them and getting them into an envelope and sealing the envelope, you'd best put on another stamp. 5-6 pages are about all that an envelope can handle, without putting it into the non-machinable stage.
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