Printer specifications are real and accurate and meaningful, but are not to be confused with image resolution. Printer ink dots and image pixels are simply very different things, and one color image pixel requires many printer ink dots. This is why we need a 1200 dpi printer (ink dots) to print an image at 250 dpi (pixels).
Q: What are the standard postcard sizes you offer? A: For flat standard postcards, available sizes are as follows: 4 x 6, 4.25 x 6, 5 x 7, 5.5 x 8.5, 6 x 9, and 6 x 11. Folded postcards have 2 kinds: half-folds and tri-folds.
Larger postcards, such as a 6 x 9 postcard, require a 47 cent stamp, but when you mail more than 5,000 postcards, the Standard Mail Presort rate is only 26 - 32 cents per postcard (exact rates depend on the addresses contained in the list) saving you 19 cents or more in postcard postage per piece!