You can use the POST /addressCorrection API to check your address list. This API will return each address in your list with 3 boolean flags: standard, international & nonmailable.
You can use this to filter out the nonMailable addresses. If you don't, our system will detect them and filter them out so that no production/postage cost is incurred on these addresses. Non-standard addresses will be printed and mailed at first class postage rate. International will be mailed at international postage rate.