POSTNET (Postal Numeric Encoding Technique) encodes a US numeric address code (also called Zip code) which may contain 5, 9 or 11 digits - frequently referred as Zip, Zip+4 and Zip+6.

POSTNET is a height-modulated symbology which encodes the data in the height of the barcode instead of the width. Barcode DLL produces POSTNET barcode based on USPS standard. The height of each bar and the pitch between two adjacent bars are fixed and can not be modified - changing NarrowBarWidth and BarHeight yields no effect. Although Barcode DLL produces human readable if you desire, keep in mind that USPS standard does not allow human readable text under the barcode.

Barcode DLL accepts non-numeric input but filters them out at the time of the encoding. It adjusts the length by adding trailing zeros to meet the length requirement. You may take the advantage by assigning the full address line to the Message instead of passing only digits. For example, data input Monterey Park, CA 91755-1688 yields an identical barcode as message 917551688.