Outlook 2016 doesn't accept password or app password

No warning but this is how MS operates these days. Every product, whether the OS, Office, Edge, Developer Tools,... they drop changes without much of a notice. No instructions, no whitepaper in most cases... If we are lucky, some product manager makes a blog post. Heck, it's an email account - why not use it and email us critical updates.

I work on software as well and while I understand the challenges of maintaining legacy code but things that are protocol-based are usually modularly enough to backport. I think this is how MS try to squeeze revenue whichever way it can, i.e., sell new Outlook 2021, get you to use ad-inserted version, sell your data... I do think this time things are done very purposefully - the convenience of it aligning with the "new Outlook" is hard to ignore.

I have moved my data off Microsoft platforms, bit by bit... Giving Google access to some of my data give me much higher return in terms of value! For example for Calendar, Google Calendar lists a picture of the place of the event/meeting.. and Maps alert me to leave while factor in traffic and such. Microsoft's - NOTHING! Microsoft's AI on email and calendar is also terrible. If I book a flight then cancel or change it, Microsoft's AI is too stupid to understand and insert all the wrong/outdated flight information to the calendar but Google's is smart enough to figure all of them out.

I must say that things have settled down - still getting the prompts for each account on opening Outlook 2013 but all mail functions are working.

(Unsuccessfully trying not to succumb to nostalgia for this thread.)

It depends on your account and usage pattern. I came back from an overseas business trip 10 days ago and it was prompting me constantly. After a few days, it settled down. However, on my phone, I am still getting prompted left and right, nearly constantly. I have moved most stuff off Microsoft system and working on the final bit of data, so I still have my phone logged into the account via EAS.

I think it saw the sudden change in IP address and region as a clue but it's such an antiquated way of doing things when it captured my device's UUIDs. Google is got this down to a science. Google challenges me when I feel I should be challenged but my usage, location or pattern is so out of norm. Microsoft' approach feels like some 2nd grader wrote the logic.

Now, if you look at Microsoft's strategy of auto-login into every damn app, be it Windows, Edge, Teams, Office.... all without additional password prompts, I don't get this unusual scare and care on EAS.

Any news on this?

At the moment I have permanently deleted the Microsoft accounts from Outlook 2016 and I only use the latter for a pec email from Aruba which at the moment has no problems. I access Microsoft email via web browser.