Electronic mail has significantly reduced the amount of regular mail sent daily through the post office. Although there are many advantages to using email for most business correspondence, there are still many instances when old-fashioned "snail-mail" is preferable, such as when original signatures are required. These business letters are usually more formally constructed than email messages. It is necessary to follow conventions in both the format of the letter and the way the letter is folded to fit into a business-sized envelope.
Place the letter flat on the table, right-side up. Place the ruler along one of the sides of the letter. Align the end of the ruler with the top of the page. Lightly fold the bottom edge of the letter up until it meets a place on the ruler that is one third the length of the letter from the top edge. For example, if the length of the page is 11 inches, 1/3 from the top of the page will be 11 inches divided by 3 = about 3.5 inches. Do not yet press this fold firmly.
Fold the top edge of the letter down until it meets the folded edge made in Step 1. Align all the edges of the letter, making sure they are all perfectly straight. Firmly crease the paper along both folded edges.
Hold open the flap on the business envelope with one hand. Hold the letter in the other hand, so that the top part of the letter will be at the top of the letter. Slide the letter into the envelope. Insert one bottom corner of the long end of the letter into the mouth of the envelope, then the other side, if the envelope is the type that has the opening on the longer side. Insert one short end of the letter into the mouth of the envelope if the opening is on the short end of the envelope. Seal the envelope.
When using envelopes that open on the short end, it is easier to insert the letter if you hold the envelope slightly open by placing your thumb and forefinger on each side of the envelope and slightly bring your thumb and finger towards each other. This will widen the opening of the envelope.
Handle the paper carefully or you could get a paper cut from the edges.