SALT LAKE CITY—A man in Emden, Mo., recently mailed a letter that he had addressed, in a scribble, to somebody in "Shelhjreille, Mo." That's the way his handwriting made it look, anyhow.

The letter was delivered the next day. Gary Oliver, a postal clerk 1,200 miles away, got it there. Mr. Oliver works in the Salt Lake City "Remote Encoding Center" of the U.S. Postal Service—a room where hundreds of clerks sit in silence, day and night, staring at America's worst-addressed envelopes.

...