Automated mail processing machines read addresses on mailpieces from the bottom up and will first look for a city, state, and ZIP Code. Then the machines look for a delivery address. If the machines can't find either line, then your mailpiece could be delayed or misrouted. Any information below the delivery address line (a logo, a slogan, or an attention line) could confuse the machines and misdirect your mail.

Use the following guidelines:

• Always put the address and the postage on the same side of your mailpiece.
• On a letter, the address should be parallel to the longest side.
• All capital letters.
• No punctuation.
• At least 10-point type.
• One space between city and state.
• Two spaces between state and ZIP Code.
• Simple type fonts.
• Left justified.
• Black ink on white or light paper.
• No reverse type (white printing on a black background).
• If your address appears inside a window, make sure there is at least 1/8-inch clearance around the address. Sometimes parts of the address slip out of view behind the window and mail processing machines can't read the address.
• If you are using address labels, make sure you don't cut off any important information. Also make sure your labels are on straight. Mail processing machines have trouble reading crooked or slanted information.

TIPS
--Always put the attention line on top -- never below the city and state or in the bottom corner of your mailpiece.
--If you can't fit the suite or apartment number on the same line as the delivery address, put it on the line ABOVE the delivery address, NOT on the line below.
--Words like "east" and "west" are called directionals and they are VERY important. A missing or a bad directional can prevent your mail from being delivered correctly.
--Use the free ZIP Code Lookup and the ZIP+4 code lookup on the Postal Explorer website (left frame) to find the correct ZIP Codes and ZIP+4 codes for your addresses.
--Almost 25% of all mailpieces have something wrong with the address -- for instance, a missing apartment number or a wrong ZIP Code. Can some of those mailpieces get delivered, in spite of the incorrect address? Yes. But it costs the Postal Service time and money to do that.
--When a First-Class Mail letter is square, rigid or meets one or more of the nonmachinable characteristics it will be subject to a nonmachinable surcharge.
--Sometimes it's not important that your mailpiece reaches a specific customer, just that it reaches an address. One way to do this is to use a generic title such as "Postal Customer" or "Occupant" or "Resident," rather than a name, plus the complete address.
--Fancy type fonts such as those used on wedding invitations do not read well on mail processing equipment. Fancy fonts look great on your envelopes, but also may slow down your mail.
--Use common sense. If you can't read the address, then automated mail processing equipment can't read the address.
--Some types of paper interfere with the machines that read addresses. The paper on the address side should be white or light in color. No patterns or prominent flecks, please! Also, the envelope shouldn't be too glossy -- avoid shiny, coated paper stock.

Publication 28 - Postal Addressing Standards.

Quick Service Guide 602 - Basic Addressing Standards.

Return Address

Special Addressing Services (Ancillary Service Endorsements)

Additional Resources

Source: USPS http://pe.usps.com/businessmail101/addressing/deliveryaddress.htm