All US addresses created through POST /v1/addresses and all inline addresses for POST /v1/postcards, POST /v1/self_mailers , POST /v1/letters, and POST /v1/checks will be automatically standardized, cleansed, and verified through our Address Verification API before being returned back to you in the API response. All international addresses will simply be standardized by being transformed to all uppercase to conform with USPS standards. Whether or not we will allow you to create successful postcards, letters, or checks depends on your Strictness Setting.
This functionality occurs in both live and test mode, and is provided for no additional cost with your postcard, letter, or check subscription.