In 1983, the U.S. Postal Service introduced ZIP+4®, which adds four digits to the basic five-digit code as an extra identifier to improve the mail sorting and delivery process. ZIP+4 can help identify a geographic segment within the five-digit delivery area, such as a city block, a group of apartments, an individual high-volume receiver of mail, or a post office box, for example. The USPS provides the following example to define the number groups that make up a ZIP+4 code:
The nine digits of a ZIP+4 code (e.g.,12345-6789) may be grouped as follows:    
Besides ensuring mail deliverability, businesses and organizations can benefit from ZIP+4 in other ways. One example is in the healthcare industry, where adding +4 aids in HIPAA compliance. In 2012, HIPAA Version 5010 became mandatory for all electronic administrative transactions in the U.S. healthcare system, such as eligibility, claim status, referrals, claims, and remittances. The requirement applies to all HIPAA-covered entities including health plans, clearinghouses and healthcare providers who conduct electronic transactions. To be HIPAA 5010 compliant, all transactions must include the actual street addresses of the service facility and billing provider, plus their complete 9-digit zip codes.
Melissa has decades of experience as a leading address management and mailing solutions provider. Our Address Verification service CASS processes your mailing list by matching the addresses in your mail file to the monthly updated USPS® National Address file, adding the correct ZIP+4 postal codes and standardizing to meet USPS CASS requirements. Melissa is a CASS and PAVE Gold Certified USPS Partner and NCOALink Full Service Provider Licensee.