The U.S. Postal Service provides a suite of USPS Web Tools that can be used to validate or find mailing addresses, track and confirm mail delivery, calculate shipping rates, and create domestic or international shipping labels.
The Domestic Mail Service Standards APIs can help predict when a package will arrive at its destination. APIs are available for Priority, Package (which includes Standard Post Bound Printed Matter, Library Mail and Media Mail) First Class, and Express Mail types. The USPS reiterates that these are predictions, or standards, and not guaranteed dates.
The following is a list of SDKs from our SDK directory that matched your search term. Though your definition of an SDK may differ, in our world, we define SDKs as platform- specific tools for consuming existing APIs of the sort we list in our API directory. For example, the Ruby SDK for consuming the Twitter Ads API. If you think an SDK, API, or other asset is missing from our directory, be sure to check our guidelines for making contributions to ProgrammableWeb.