Outlook 2016 doesn't accept password or app password

Again, Microsoft managed accounts!!! Microsoft has been pushing this on small to mid-size businesses. Our entire company's email is managed by Microsoft through Office 365 (now Microsoft 365) for Business. We are paying them a hefty amount because I see it in my operating budget for the teams that report to me.

I have deleted my email account and re-add the account, and am using the latest version of the client. Just to de-wrinkle one element, I even downloaded Outlook for Android, which is not my favorite, and it still has the same issue. And to put into context, I am a developer with in-depth knowledge, so please don't assume those of us haven't tried things you are suggesting.

I can tell you have very minimal experiences on this because with Microsoft-managed accounts, our in-house IT has very very very limited options in terms of infrastructure level settings or issues - they are ALL controlled by Microsoft.

Now that you mention it the amount of spam originating from Microsoft, which is by far the greatest offender in my experience, specifically from Microsoft Azure and Microsoft Tenant IPs identified in email headers, has also reduced in the last couple weeks, presumably by spammers also experiencing this issue. I used to report hundreds of spam messages to the Microsoft CERT team before giving up because they were evidently unable to make any significant headway to get on top of it. Rarely get spam originating from Google.

How do we get MS to reopen the issue? They say fixed on 2 Feb but issues still constantly occurring

I'm using Outlook 12.0.5603.1000 and still having issue

From not the community crew:

Since the folders of my 3 MS free personal outlook.com suffix accounts missing on the outlook.live.com and New ooutlook on and from Jan 15, and each account became normal in a interval of around a week, the eldest hotmail period account is the last one becoming normal on around Feb 3.
If the outlook.live.com and new outlook were already on Microsoft cloud or Native Microsoft sync, and remain the basic authentication.
The loading page address of the outlook.live.com have something like *ppsecure*, not the *oauth* as while logining the https://answers.microsoft.com/
I used the New outlook to login the Yahoo Japan and got them informed that I login from Malaysia several times even several days before I used it in the new outlook.
(The Yahoo Japan is not the Yahoo, but it was detect as Yahoo, and can't be logged as the default Yahoo in the New outlook. I logged in via the imap in the New outlook and outlook 2021.)
I wonder if the outlook 2021 were already logining through the Microsoft cloud or something alike, since I used to login The Yahoo Japan via the outlook 2021 imap around that period of time around August 2023 .

https://learn.microsoft.com/en-us/exchange/clients-and-mobile-in-exchange-online/deprecation-of-basic-authentication-exchange-online
Article 08/31/2023
We removed the ability to use Basic authentication in Exchange Online for Exchange ActiveSync (EAS), POP, IMAP, Remote PowerShell, Exchange Web Services (EWS), Offline Address Book (OAB), Autodiscover, Outlook for Windows, and Outlook for Mac.

https://techcommunity.microsoft.com/t5/microsoft-365/native-microsoft-sync-technology-migration/m-p/436039
Ross Smith IV replied to Anthony Russell ‎Apr 12 2019 06:40 AM For Outlook mobile, major feature deployment operates with a staggered rollout where we begin with consumer accounts (if applicable) and then deploy to commercial accounts like Office 365.

Ross Smith IV replied to Anthony Russell ‎Jun 25 2019 07:58 AM

We've now migrated all O365 tenants to the native Microsoft sync technology.

https://learn.microsoft.com/en-us/exchange/clients-and-mobile-in-exchange-online/outlook-for-ios-and-android/outlook-for-ios-and-android
Article 02/22/2023
The native Microsoft sync technology that Outlook for iOS and Android is adopting has been in use by the native Windows 10 mail client for a number of years, and in the future, will be used by Outlook for Mac.

https://support.microsoft.com/en-us/office/sync-your-account-in-outlook-to-the-microsoft-cloud-985f9e19-d308-4e85-9d1d-0c6f32f8e981
Sync your account in Outlook to the Microsoft Cloud

Outlook 2021 for Mac Outlook 2019 for Mac Outlook 2016 for Mac Outlook.com New Outlook for Windows Outlook for Android Outlook for iOS Less

Article updated: May 2023

To enhance your Microsoft 365 experience in New Outlook for Windows, Outlook.com, Outlook for iOS, Outlook for Android, and new Outlook for Mac, you can now sync your non-Microsoft accounts (including their emails, contacts, and events) to the Microsoft Cloud. This is available for Gmail, Yahoo, iCloud, and IMAP accounts in Outlook for iOS, Outlook for Android, and new Outlook for Mac. Also available for Gmail and Yahoo accounts in New Outlook for Windows and available for Gmail accounts in Outlook.com. This allows you to enjoy many features that were previously only available to those with Microsoft 365, or Microsoft Exchange Online email accounts.