The proper way to stuff an envelope is to place the printed side of the mail so that it faces the recipient. The simplest way to do this is to fill an envelope with the printed material facing its flap. Insert folded mail with the final crease facing the front of the envelope.
Window envelopes should be stuffed with the address of the recipient facing outward through the window. Ensure that the entire address, including the zip code, is visible before sending the mail. The proper size should also be considered when stuffing an envelope. Small business envelopes may be used for personal correspondence and bill coupons, while longer, number 10 envelopes are useful for long letters and business mail.
Letters should be folded face-up, starting with the top of the paper going downward. The fold should be slightly less than one-third down the page to create the first crease. The final crease should be folded up over the top half to create an even rectangle shape before inserting in the envelope. When mail must be folded to fit into a small envelope, fold it three-quarters from the bottom to the top. Fold the document again one-third of the width from right to left. Finish the fold by neatly creasing the left side in, and insert it in the envelope.