Outlook email keeps prompting for a password, and then not accept it. Blocked out of emails.

I spoke too soon. The "Send NTLMv2 response only" policy no longer works. I'm back at the same state with Exchange Server and Outlook. However, I noticed the Exchange servers started to issue NETLOGON event 5719 the time of the failure indicating they cannot communicate with a domain controller. Once this event is logged, DCOM events are also logged related to contacting the other Exchange servers. Restarting the NETLOGON service does not fix the issue as the event is continued to be raised. Microsoft has acknowledged there is some issue with Windows Server 2025 domain controllers in another case I have open, but the workaround they provided me for that case does not work here (resetting the computer machine password with reset-computermachinepassword).

This is a real annoyance!!!

You might want to create a new thread and ask that question again, as that support specialist was asking the original poster for that information.

1 - Mailbox extension: Outlook

2 - Mailbox is for personal use

3 - The problem is on my iPhone (SE).

  Outlook is still accessible and working fine on two computers, a desktop as well as laptop.

  both utilizing Office 2010 Professional

4 - Not sure how the mailbox is configured on my iPhone.

I have both old and new Outlook apps on my phone, and they have both been working just fine.

I prefer the older Outlook, simpler to work with.

About a month ago, I was somehow signed out of both apps on my iPhone, and have been unable to access either one. When entering my password, I receive the following "statement" in RED:

"Your account or password is incorrect. If you don't remember your password, reset it now" (last three words in blue). I have been unable to reset my password, as it required an "Authenticator" Code, indicating that I have two-step authorization enabled, which I did NOT set up. Furthermore, I have the Microsoft Authenticator available, but that app won't accept my MS password either.

For me, I have the solution. After upgrading Exchange 2019 to CU15 you have to add the policy setting “Network security: LAN Manager authentication level” to “Send NTLMv2 response only" on all Exchange Servers. It was a little difficult for us because we were also having an issue with authentication due to a known issue in Windows Server 2025 DC's that we are waiting for an update to fix. I also could not successfully use CU14 and CU15 servers together without this authentication issue. After upgrading all to CU15 and adding the policy setting they all were able to work successfully.

Wow, thanks very much for this solution, it worked straight off the bat.

I'd been having the Windows Security password prompt pop up every time i used Outlook Classic on my laptop, although it didnt have the same issue with Outlook NEW.

Why I use classic outlook though, you might ask, is that its much easier to copy and paste emails / attachments from my Classic Outlook inbox to my PC/One Drive folders as its much more difficult with Outlook NEW for some reason, too many other stages to go through.

This issue arose on my Win 11 laptop, which I don't use all the time and hadn't noticed that the mail folders for my two "live.com" work email accounts hadn't updated in over a week,

A message in status bar of Outlook on both these accounts said " folder last updated 21/02/25", and "Need password"

Also a separate pop up dialog box, similar to an email notification dialog box, asking for email password would pop up in right hand bottom corner of screen, where the clock/date bar is .

However, changing the HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Common\Identity - EnableADAL registry key from [0] to [1], as suggested by NS_358 immediately cured the problem.

Shut down Outlook Classic, fired it up again, no password prompt boxes popped up and it happily updated both my MS work mail accounts ("Work/School" accounts rather than "Personal" email, just to clarify) Many thanks, genius !!!