What do the different US Mail Strictness Settings do?

Depending on what business logic you’d like to take based on your verification result, you can toggle your US Address Strictness Settings in your Dashboard. There are 3 possible Strictness Levels:

• Strict: Only US addresses that Lob and the USPS deem deliverable can be successfully used as the to address for postcard, letter or check resources. Postcard, letter, and check requests sent with non-deliverable addresses will return a 422 (Unprocessable Entity) error. This maps to a deliverability value of deliverable (see documentation). If addresses have never been run through verification (i.e. were created in the past), they will also err when used as the to address.
• Normal: Postcards, letters, and checks will be created for addresses that Lob and the USPS deem deliverable, as well as addresses for which secondary information is extraneous or missing. Otherwise, you will receive a 422 (Unprocessable Entity) error. This maps to the deliverability values of deliverable, deliverable_unnecessary_unit , deliverable_incorrect_unit and deliverable_missing_unit (see documentation). If addresses have never been run through verification (i.e. were created in the past), they will also err when used as the to address.
• Relaxed: All postcard, letter, and check resources will be successfully created and mail delivery will be attempted, regardless of address validity. You will not receive a 422 (Unprocessable Entity) for Address Strictness reasons.