Sending personal letters was replaced by emails years ago, at least for the most part. Business letters are still being sent and therefore there is still a need to know how to properly address an envelope. Addressing an envelope properly helps get your letter to the correct destination on time.
To address an envelope, print the return address neatly in the upper left-hand corner of the envelope.
Begin by writing the sender's name and/or the company's name on the first line of the address.
Add the sender's street address (include Ave., St. or Blvd., as well as apartment, office or suite number) or post office (P.O.) box number on the second line.
Include mail-stop numbers, for mail distribution within a large company, where an apartment or suite number would appear on the second line.
Print the city name followed by a space, the two-letter capitalized state abbreviation and the ZIP code (five-digit or ZIP+4) on the third line.
Include the country name, if necessary, in capital letters on the fourth line of the address.
Print the mailing address (the destination address) in the center of the envelope or package, putting each element of the address in the same order as outlined in Steps 1 through 6 above.
Attach proper postage to the upper right-hand corner of the envelope, on the same side of the envelope as the destination address and return address.
Use the ZIP+4 to help speed delivery of domestic mail. To correctly address an envelope to a member of the military, use the recipient's grade and full name (including middle initial or middle name) on the first line. On the second line, write the PCS number, unit number or ship name. On the third line, military addresses use an APO (Army Post Office) or FPO (Fleet Post Office), then a regional designation such as AE (Europe, the Middle East, Africa and parts of Canada), AP (the Pacific) or AA (the Americas and parts of Canada); followed by the ZIP code. Address the envelope before inserting the contents, so that you are writing on a flat surface, and don't ruin any photos or documents you may be sending.
Avoid placing tape over postage stamps. Postal processing equipment can't read the ultra-violet ink on a covered stamp and will return your mail. Use a pen! Address your envelope with bold printing using a pen with waterproof ink, just in case.