I went to the post office and talked to the guy who handles bulk mail. He said that it has to be larger than either 6 1/8" wide or 11 1/2" long. So 6 1/2" x 8" postcards will be acceptable. We also went over the layout and made sure I had evetything right. All I had to do was resize the existing image and ordered them from got print.
More equipment then I know what to do with.