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Many professionals opt for configuring their Office 365 account with MS Outlook to double their productivity. But while doing so, one of the most common issues that they face is Outlook continuously prompts for Office 365 credentials. And if the user cancels the credentials prompt, they receive an error message saying-

The connection to Microsoft Exchange is unavailable. Outlook must be online or connected to complete this action.

It occurs mostly when the user is trying to access the cloud mailbox in the Outlook application after the Office 365 migration. It is frustrating for the user since they cannot configure or even access the cloud account in the Microsoft Outlook application since this prompt flashes continuously. One main reason behind this issue is that the setting of Logon network security setting of the Microsoft Exchange dialog box is set on something else other than Anonymous Authentication. So, how can this issue be resolved? In this article, we will tell you about all the possible methods to solve this error.

Methods to Fix Outlook Credentials Prompt Issue

There are several methods to resolve this issue. Here we have mentioned some of the most effective ways:

  1. Update Office 365-
    One of the first things you should do to solve this issue is update Office 365 and Outlook to the latest available version. Updates focus on getting rid of all the tiny bugs which the older versions have and tend to provide improvements.
  2. Try to remove and reset your account credentials.
    Go to “Control panel,” select “Credential Manager,” and clear any cached credentials.
    Go to Control panel
  3. Change the Registry for Modern Authentication.
    You can create or change the registry key so that Outlook start using the new authentication method for web services, such as EWS and Autodiscover. To do this, follow the below steps:

    • Close MS Outlook and start Registry Editor by typing regedit.exe in the Run dialog box.
    • Find the appropriate registry path according to your Outlook version. In outlook 2016, you can find it here:
      Find the appropriate registry path according to your Outlook version
    • Now, click “Edit” in the menu tab and select “New,” and then click “DWORD Value.
      Click on Edit in the menu tab
    • In the DWORD Value, type “AlwaysUseMSOAuthForAutoDiscover” and click “Modify.”
    • Now, type 1 in the value data box and click “Ok.” Exit registry editor to finish the process.
  4. Change the “Login network security” settings to “Anonymous Authentication.”
    Note: This method applies to Outlook 2013 (some builds) and earlier versions of MS Outlook.
    • Go to “Control Panel,” locate and select “Mail.” A new wizard will appear on the screen: select “Show Profiles.”
      In Controle Panel locate and select Mail
    • Select the Outlook profile and click Properties, and then select E-mail Accounts.
    • Now, select the desired profile and click Change.
      Select the desired profile and click change
    • A new wizard will appear on the screen: click “More Setting” to open the Microsoft Exchange dialog box and then select the “Security” Tab.
      Open the Microsoft Exchange dialog box and select the Security Tab
    • In the “Login Network Security” list, select “Anonymous Authentication” and then click “OK.”
    • Now, finish the process by following the instructions and close the Account settings dialog box.
  5. Check the Checkbox “Remember My Credentials
    When you receive the Outlook credentials prompt on the screen while opening MS Outlook, you’ll see that there is a “Remember my credentials” checkbox below the credentials field. Make sure you tick that checkbox so that you don’t face this issue again and again.
    This way, MS Outlook will remember your credentials, and you might not face this problem again.
  6. Using a Group Policy
    Sometimes, this error appears due to a wrong Group Policy. You can either enable or disable group policy for your Exchange account.

    • Go to Policies>>Account Settings>>Exchange>>Authentication with Exchange Server.
    • In the Settings section, select the authentication with Exchange Server.
    • You will find multiple group policies for authentication, such as:
      1. Kerberos/NTLM Password Authentication
      2. Kerberos Password Authentication
      3. NTLM Password Authentication

    To disable any of these group policies, select Not Configured under the ‘Authentication with Exchange Server’ section.


Facing the “Office 365 Credentials Prompt” continuously can annoy any user to the extent that they would want to uninstall Outlook from their system or even stop using it. Hence, fixing this issue at the earliest is crucial since most of the work is done through it. By using the five methods which have been mentioned above- updating application/platform version, resetting account credentials, modifying Windows Registry, changing login network security settings, editing Group Policy settings, you can fix this error in no time.

Generally, the credentials related error due to manual migration where the connection between the platforms is not fixed properly. So, you must use a professional migration software for moving Office 365 mailboxes between different accounts.

Kernel Office 365 Migration software can migrate mailbox without affecting the credentials. The mailbox will move to an existing mailbox in a different account, and you can access it by using the existing account credentials.