The attention line should be the first line of the address in the center of the envelope. This is necessary because automated processing machines start reading addresses at the bottom of envelopes, searching for cities, states and zip codes. Improper format slows mail delivery.
Following the name or attention line is the business name, if required. After that comes the delivery address. The city, state and zip code are all placed on the last line.
To promote the processing of mail, letters should be addressed using all capital letters but no punctuation marks. There should be only one space between the city and state but two spaces between state and zip code, according to the U.S. Postal Service.