I did not use an oversized envelope. I used a plain white business envelope which has the security printing inside so you cannot see through it. I triple folded a piece of white 8.5 x 11 typing paper and inserted three 20's and a 5 inside the folded paper. Sealed it and installed (1) FOREVER stamp on it. I assumed that the 4 bills and one sheet of paper would fly first class no problem. Plus if it was over weight, it would have gotten returned to me because I had a clear return address sticker on the envelope.