Outlook 2016 doesn't accept password or app password

I tried IMAP and it worked. We don't have very severe restriction on adding additional email accounts. I think we still have some accounts hosted on on-premise Exchange servers while our "work emails" were moved to Exchange Online.

From not the community crew:

Just found a difference which I don't know why they are different. Since my outlook 2021 and 3 of my personal free outlook.com address are all MSA* not the Bearer*. And it should be via Mapi over http. (Hold the control button and right click the outlook icon in the down right corner system tray.)

And it seems that if I add the ExcludeExplicitO365Endpoint in the registry, while add the account via the autodiscover in the mail(Micorosft outlook) classic layout in the control panel will be configured as imap account. (While adding the accounts via the modern layout seems did not affect.)

https://learn.microsoft.com/en-us/outlook/troubleshoot/profiles-and-accounts/unexpected-autodiscover-behavior
ExcludeExplicitO365Endpoint

https://techcommunity.microsoft.com/t5/exchange-team-blog/basic-auth-and-exchange-online-february-2020-update/bc-p/1205485
 ‘Bearer*’ means Modern Auth – ‘Clear*’ means Basic Auth.

https://learn.microsoft.com/en-us/outlook/troubleshoot/connectivity/description-of-the-connection-status-dialog-box
Authn

Indicates the authentication type that a given Outlook connection uses. Possible values include:

ERROR
CLEAR - (Outlook uses clear to indicate basic authentication - typically used together with SSL)
NTLM
NEGO
KERBEROS
ANONYMOUS
AUTOLOGON
.

This is a third party site.

• https://office-watch.com/2022/discover-mailbox-connection-details-outlook/
  The method of authentication used. Meaning how Outlook passes your credentials to the mailbox.

CLEAR  or Clear*- (meaning Basic Authentication which is being turned OFF for Microsoft hosted mailboxes and needs updating)

NTLM

For older Exchange Server connections we’ve seen CLEAR (NTLM)

NEGO

KERBEROS

ANONYMOUS

AUTOLOGON

Not documented by Microsoft properly but used with Microsoft hosted mailboxes are:

MSA* meaning MicroSoft Account login

Bearer* denotes Modern Authentication

Very interesting... So with your Outlook 2021, and without the ExcludeExplicitO365Endpoint regkey, you were able to use auto-discovery to add your Hotmail accounts as IMAP, right? Are your email/contact/calendar sync or just email sync?

This is exactly what I have asked before: Does outlook.com support EAS connection with OAuth for PERSONAL accounts? And I did not get an answer from both, David and Gabriel. I was not able to find any documentation from microsoft that cleary states this.

As you already mentioned I also found out that EWS will go EOL in the near future, but not EAS.

It would be very helpful to have an overview over what protocols are supported (with oauth) for personal accounts with/without M365 subscription.

Just as a reminder: We all want to have a protocol/connection type that supports oauth AND have at least eMail, calendar and contacts synch. Of course all data supported by EAS would be nice.

From Not the community crew:

I only found it once.
I used to add the ExcludeExplicitO365Endpoint =1 once, and the setting remain unchanged for several months around Nov 2023 -Feb 2024.
I just found it in the outlook account window was as imap once time just after adding the account via the Mail in the control panel. It happend around Jan or Feb 2024.
And I just delete it and delete the ExcludeExplicitO365Endpoint and recreate the accounts via the classic outlook.

Most of the time, I only use the mail in the control panel to create profile only.
Most of the time I add the accounts via the classic outlook.

The accounts are listed as Microsoft Exchange in the account window in the outlook in my usually creating account process, and should be via MAPI over http.
I don't know if the way use the EWS or not, but I always set the "Turn on shared calendar improvements" which should be rest API or somthing.And the It will be showing checking the contacts folder in the tray while opening the outlook.

I did not know how the autodiscovered imap outlook account behaves since it should only sync mail, and I delete it right after found it is imap.

I just wonder that if the "ExcludeExplicitO365Endpoint"=1 and the IMAP account autodiscovered mean that there are servers are not as office365endpoint but still offer imap autodicover via the personal outlook.com address around Jan or Feb 2024.

And I only add one account each time, it should be my oldest account created in the homail period, but lost the hotmail.com suffix during the live.com to outlook.com period.
I did not know how my live.com period account and outlook.com period account behave. (3 of them are all have only outlook.com suffix now.)