Aside from the very changeable and varied customs for letter writing in the United States, there are a few rules about the envelope itself that are followed, in everything from personal correspondence to business letters and bills. I call these rules protocols, because they are neither official rules or regulations, nor matters of etiquette, but simply protocols, a system of presenting information in a standard way that people expect. These protocols are fairly simple, so simple that it may be hard to imagine doing anything any other way. However, they are hardly sent down by Heaven, in fact, if you peruse the official USPS FAQ, at the rather unwieldy address of http://hdusps.esecurecare.net/cgi-bin/hdusps.cfg/php/enduser/faqs.php
you may find information on "duck stamps", and mailing shotguns, and whether it is okay to tip your delivery person, but you will not find information on how to address and stamp and envelope. However, by custom, in the United States:

  • A letter is always mailed with the the address written parallel to the longest side. The address is usually written in about the exact center of the letter. The postal service would probably deliver a letter with the address written perpendicular to the longest side, but it may cause delays.
  • The stamps are always put on the same side as the address, and they are always put into the upper right hand corner. Due to the US Postal Service's many different stamps, and often changing rates, letters may at time take quite a collection of stamps, however, it is a good idea to use as few as possible and not to let them flow and flood all over your letter's face, even though again, it is still deliverable as such.
  • The return address, which is almost always included, is put on the front side of our letter, in the upper left corner. This is the first place in which US Postal protocol seems to not be universal or obvious: I have noticed that in other countries, the return address is often put on the opposite side of the letter, and that some people in this country occasionally prefer this scheme.
  • In the United States, almost all envelopes stick either with saliva, or have a self-sticking mechanism. Therefore, it is unusual to put anykind of tape or sticker across the back of envelopes, although I have seen both done, either because someone has an envelope that has lost its stickiness, or purely for artistic reasons. I have, on occasion, even received a wax-sealed letter.
  • Finally, letters are almost always mailed so that the flap starts along the upper side of the letter, the same edge that has the return address and the stamps.

So, here we have had to describe at some length five rules for addressing, stamping and sealing an envelope, something that most of us take for granted. Again, these rules are not , as far as I can tell, enforced, yet they are universally known and followed. Some of them are variable, but make little differences. It is interesting that one piece of envelope protocol is actually counter-productive, namely, the last one. Years ago, on a lark, I decided to mail all my letters "upside down", so that the flap was on the bottom of the letter. I realized that there is actually a practical reason for doing this: when you are opening a conventional letter, there is a good chance that it will tear, ruining the return address, and also the stamp. Addressing envelopes upside down minimizes the chances of this happening.

But, in any case, if you have just dropped down to this country from somewhere far away, perhaps outer space, you now know how to mail your letters.