Outlook 2016 doesn't accept password or app password

Ticking doesn't seem to matter - the AI theory seems more plausible than anything. It's too random.

So wait a minute, you're saying you TICKED the box to save the password and it worked!
But for me, I UNTICKED the box and it worked.

hmmmm, I wonder if they're testing AI for authentication?

How the hell else can any technical issue be this completely random?!?!?!

It's like this for almost 2 months.....

Problem is, MS de facto depreciated outlooks 2013-2019. Not sure about 2021, but i am not in the mood for testing it out at my expense. I feel this all about pushing more AI into masses. Which is absent from non 365 Office. Can't think of any reason why having copilot in all other places is not enough. It tracks you in windows, it tracks you in Edge, it tracks you in all other places where you use MS services online. That and one drive integration which is also subscription/data mine for them. Google put utility to work around Outlook vs GMail limitations back in the days and i don't see why MS can't pull something similar. They did add utility to Outlook 2010 to work with modern protocols of MSN/Live/Hotmail etc. back in the days. So it's not impossible. It just don't bring them any money only customer appreciation and loyalty.

A few days ago, as one of my accounts stop receiving emails on my Outlook 2013. I deleted it thinking that it would be interesting to see if, by re-adding it, things might correct. Sadly, Outlook wouldn't allow me to re-add the account.

After reading your message I gave it another go just a while ago, repeatedly entering the password. However, in my case, I ticked the box to remember password and, hey presto - the account successfully re-added. Since then I've had no promptsfor my other three MS accounts.

This is such a wild issue and so random that one must conclude that something very disruptive has hit MS systems, accidentally or otherwise. And further disturbing is the fact that MS isn't coming clean about it.