As stated in the section on Envelopes a letter, especially a business letter, is folded twice into horizontal thirds and placed into an envelope.
This insures a little privacy in the letter. The letter is also easy to unfold after opening the envelope.
The following diagram shows how a letter is normally folded. Click on each picture for more.
This type of fold is used regardless of letter style.
If the letter needs to have the address face out an envelope window, make the second fold in the same location but opposite direction. The letter will then be folded in a Z shape and the address can be positioned to face out the window of the envelope.
|Unfolded||First Fold||Second Fold|
See Envelopes for more on putting letters in envelopes.