For postcards you'll notice that the postcard builder layout is actually
4.25" x 6.25" instead of
4" x 6". This extra space is what we call the bleed area. The bleed area is included to ensure that artwork gets printed to the edge - artwork gets printed with larger dimensions and is subsequently trimmed down. Although, backgrounds and graphics should be extended into the bleed area as shown with the background in the above example. Not having them extend into the bleed area could result in a white or unprinted border around the edge of the postcard.
If you would like to add an image that covers the entire postcard. An image with 300DPI would need to be 1800X1200, the image size can be made a bit bigger at 1875X1275 to help cover the bleed edge more easily.
Keep all text within the safe zone to make sure no important content is cut off.
Address Block and Postage
On the postcard, there is a space marked off as
*RED: INK-FREE AREA*. Anything in this area will not be printed to leave room for the postage and address information.