At this pointy merely the observation that the autodiscover process looks the similar from O2016 “simplified” account creation as it does from Outlook mobile.The autodiscover requests come from an MS owned server IP, not the computer/device IP. They both pass the username, but not the password even after the 401/Basic response.
After the two failed requests, they diverge:O2016 falls back to making a request for autodiscover/outlook schema from the real IP (and uses basic auth with password) Mobile allows the user to specify the activesync server name, then starts talking to it (from an MS server IP - the client only talks to the MS server - the MS server has kept the creds and does the talking to activesync from then on)
I haven’t had the time to debug much further, and it gets pretty annoying because after a couple of tries, the MS server caches the failed autodiscovery and stops trying for that domain for a while.
I expect this stuff is still in a state of flux as MS maybe works to integrate the accompli tech into desktop Office.