NetZipCode for .NET follows the US Postal Service "one component failure rule" to find a correct address match. This rule permits an address match if no more than one address component mismatch exists, where a "component" is defined as a predirectional, street name, street suffix, or a postdirectional.

Consider the following address: 100 E MAIN ST N

This address has all four components. If one of the components has to be added, changed, or deleted to achieve a unique match, NetZipCode will correct the address and return the ZIP+4. Under current USPS address matching rules, if more than one component is incorrect, no match is allowed. If adding, changing or deleting a component results in multiple matches, no match can be returned. The priority is to add a suffix first, before adding a directional. If there is no match, change or delete the suffix. Finally, change or delete a directional.

If there is no exact address match within the city, NetZipCode applies the "one component failure rule" within the input ZIP code. If there is still no match, then NetZipCode applies the "one component failure rule" to all addresses within the postal finance number. If there is still no match, the address is rejected.

An array of flags is returned for each address giving you important information about the status of the matching process such as why the matching failed or what corrections were necessary in order to achieve a match. Also returned is the Address Type allowing you to identify Street, Military, PO Box, Rural Route, Highway Contract or General Delivery addresses and process them accordingly.