Flights on Boutique Air (4B) can now be credited to Mileage Plus:
https://www.united.com/ual/en/us/fly...tique-air.html
Furthermore, UA is actually codesharing with 4B on several routes; not only some of the old Great Lakes routes out of Denver, and the ATL-MSL-BNA route mentioned earlier in the thread, but also MSP-TVF (Thief River Falls, MN) and PDX-PDT (Pendleton, OR):
https://www.routesonline.com/news/38...late-may-2018/
Given the number of non-earning fare classes listed, I'd be curious to hear about peoples' experience booking the codeshare flights.
Press Release:
https://www.boutiqueair.com/news/271