Originally Posted by amma
Yes, it has to be less than 1/4" thick. However, you can stack them in the envelope side by side :wink: :D:D:D
Here is a link to check out the limits -- Maximum envelope size is 6 1/8" high X 11 1/2" long. There is a surcharge for lumpy or over 1/4" thick. There is a change in April 2011. The extra ounce and surcharge will increase to .20, letters will stay .44.
http://www.usps.com/prices/first-class-mail-prices.htm