The service or library that cleans the address needs to be callable from a custom .NET wrapper service or library. There is no UI requirement to display a map, or track delivery of a physical package to a postal address.
https://www.usps.com/business/webtools.htm is out as an option because the terms of use are restricted to applications supporting the physical delivery of packages.
It seems that both google and Bing have terms of use that restrict application development usage to presentation of maps in a UI.
Here's an example of using google JavaScript library for geocoding address lookups. It seems to work well. Unfortunately I can’t use this, but looking for something that works nearly as well.