Outlook 2016 doesn't accept password or app password

I mentioned this issue in my previous comment. I am on Office 365 (I guess it's called Microsoft 365 now) for business. I have issue with this work account in addition to my personal Hotmail account. In my case, on around 1/23 when the issue started, I got kicked off and had to relogin with the 2FA process. In previous 2FA login, there is a checkbox for "...don't ask again for 365 days..." and it was checked but it appears that was ignored and had to relogin. After which while I didn't get the prompt for password on this work account, it was clear I was NOT getting email pushes or calendar/contact syncs. While working on my computer, I was getting emails frequently but not a whisper on my phone.... then I get a gush of emails on my phone like dozens and dozens all at once. I have been saying this issue impact business/paid accounts as well except it seem to cause sync issue more than password issue.

All I can say is Microsoft is A MESS lately... I left the US at the onset of this issue and I am about to end my 2-week oversea trip and the issue is still not fixed.

Hello everybody,

I am wondering if some of you are Microsoft 365 customers and are having issues with Outlook.

We are a company with approx. 6500 users and some of them have issues.

When we force a reconnect of the internet connection, then the issue is sometimes solved immediately, sometimes the reconnection has to be repeated several times.

That matches with some earlier posts, stating, that only some portion of the Exchange Online Cloud Endpoints are affected.

So we suspect that this issue here is also our issue but we are not sure.

According to MS this is not related to any planned elimination of authentication protocols, etc. If you are using app passwords you should be all set, but most are still seeing the problem. When you reset your network or DNS, you get connected to a new server, and it seems some servers are having the problems and some aren't. When the problem happens for me, I have to bounce the network once or twice and it will go away as I get a new server that has the fixes applied.

The best way to go is modern authentication, but not all apps support that, at least not for outlook.com addresses.

Bounce your network connection (let it stay down for 30 seconds) and see if you can reconnect, may have to try it a couple times.

The reason it works if you keep hitting OK is eventually it tries another server (as you've likely gotten temporarily blocked from the server you were retrying to repeatedly, a security feature) and happens to get one that works that next time.

Core i14 is out now. My core 2 (not i2) is basically generation 0. No problems with it, outlook has been fine.

I've been having the same issue..
Fixed for a few days and then came back as noted by others..

I'm using emClient and connecting using Exchange (EWS) and app passwords.

Just wanted to add that if I keep pressing ok on the password prompt after multiple attempts I eventually get connected and then works ok for hours.. Unless i flush dns, or restart my network adapter which then asks for password again.

Funny thing is that on emClient forums they insisted and still do, that this is happening because Microsoft had announced that they plan to disable all basic authentication back in 2022 and now this change is taking effect for all servers.
Microsoft and basic authentication - personal outlook accounts - Announcement - eM Client
Is this in any way valid? No matter how many times I tried expressing my doubt on this they kept replying the same thing..
I even sent them this post by Microsoft which points to this thread while it was on INVESTIGATING status..
Eventually they suspended my account and locked that thread.. :D

In any case my guess is that if this was the case it would not work no matter how many times I tried logging in..
And also as I already said it worked just fine for two days as noted by others in this thread..