When designing a postcard or other items that you intend to mail through the United States Postal Service, there are many regulations to follow. The most important thing to consider is the clear area required for Optical Character Recognition or OCR. This allows the postal service scanners to read the mailing address imprinted on your piece and apply the barcode needed to correctly route your mail.
The diagrams below are from USPS and are their guidelines for mailers. Our design guide templates are marked to help you follow these guidelines. Generally speaking, keep your address area in the bottom right corner in the area indicated. OCR areas should not include any address information, as this may confuse the USPS software. In the dark pink area of our design guides, there should be no text or graphics greater than 7% greyscale.
The Postal Service will not mail any piece with rounded corners, so only round the corners if you intend to use the piece as a handout. Additionally, UV gloss inhibits the printing of barcodes, so we only apply UV gloss to the non-address side of a postcard.
For more information, please visit the USPS website to read their full regulations. There are also other resources to assist mail piece designers.