This is a great question and the short answer is 'many'.
For starters, we use multiple datasets, including the United States Postal Service, to validate and correct US addresses.
Why is this important? Although the USPS is a clear authority on deliverable address (by the USPS), they do not provide address data beyond this. For example, general delivery addresses do not provide the physical address of the recipient, just where they receive mail. Our Address Validation-US service is able to provide both.
Our additional data sources also allow us to enrich the address data beyond deliverability, like:
- longitude and latitude (geocoding)
- business intelligence, etc.