M365, Outlook password issues in MAC error

Maxx Blue 0 Reputation points
2026-09-13T05:28:17.03+00:00

Able to login on web with same m365 business account but it's not working on Outlook app on MAC system, tried all keychain etc steps, giving errors ADSTS...20 etc related to authentication need help

Outlook | MacOS | New Outlook for Mac | For business
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  1. AI answer

    2026-09-13T05:28:36.56+00:00

    Since web sign-in works with the same Microsoft 365 business account, the issue is likely in Outlook for Mac local authentication state or a known Outlook sign-in issue rather than the account password itself.

    Try these steps in order:

    1. Restart Outlook for Mac A known sign-in issue that caused errors such as CAA2000B and 49dvs was fixed in the service. Restart Outlook to pick up the change.
    2. Remove and re-add the account in Outlook for Mac If the account uses Microsoft 365 or Exchange with modern authentication:
      • Open Outlook for Mac
      • Go to Outlook > Settings > Accounts
      • Select Manage to remove and re-add the account
      • Sign in again when prompted
      • Verify Outlook can send and receive mail
    3. Reset Keychain permissions if prompts keep returning If Outlook or other Office apps repeatedly ask to sign in, ask for keychain access, or show Authentication Session Expired:
      • Quit all Microsoft 365 for Mac apps
      • If prompted for keychain access, select Always Allow
      • If that does not help, restore keychain permissions by following Apple’s keychain access steps from the Microsoft guidance
    4. If Outlook 2016 for Mac is in use, clear duplicate tokens from Keychain This applies specifically to Outlook 2016 for Mac repeated authentication prompts:
      • Quit Outlook and all Office apps
      • Open Keychain Access
      • Search for Exchange and delete items for the Exchange account
      • Search for adal and delete items of type MicrosoftOffice15_2_Data:ADAL:<GUID>
      • Search for office and delete Microsoft Office Identities Cache 2 and Microsoft Office Identities Settings 2
      • Reopen Outlook and authenticate again
      Warning: deleting keychain items affects all Office apps that use modern authentication.
    5. If the error is specifically 49dvs or CAA2000B An admin can check whether Microsoft Information Protection API is disabled for user sign-in in Microsoft Entra and set Enabled for users to sign-in to Yes.
    6. If support is needed from inside Outlook for Mac Go to Help > Contact Support. If Contact Support fails, reset the Apple Keychain by:
      • Closing Outlook and other Office apps
      • Opening Keychain Access from Spotlight
      • Selecting File > Lock All Keychains
      • Then File > Unlock Keychain “login”

    The strongest next step for this scenario is:

    • remove and re-add the Microsoft 365 account in Outlook,
    • then reset keychain permissions,
    • and if the displayed code is 49dvs or CAA2000B, have an admin verify the Microsoft Information Protection API sign-in setting.
    AI-generated content may be incorrect. Read our transparency notes for more information.

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  2. Kien 1,060 Reputation points Independent Advisor
    2026-09-13T06:19:53.1833333+00:00

    Dear Maxx Blue,

    To ensure I understand your request correctly and to support you as effectively as possible, I need more specific information from you:

    Could you share a screenshot or the complete error message such as the exact AADSTS error code?

    Which macOS version and Outlook for Mac version are you using? Also confirm whether Outlook is the New Outlook or Legacy Outlook.

    When did the issue begin, and was Outlook working previously with this account on the same Mac?

    Does the issue affect only this Microsoft 365 business account, or do other organizational accounts also fail in Outlook on this Mac?

    Can the same account sign in successfully to another Microsoft desktop application on the Mac, such as Word, Excel, OneDrive, or Teams?

    Does the account work in Outlook on another computer or mobile device?

    At which point does the occur: when adding the account, after entering the password, after MFA approval, or when Outlook starts synchronizing?

    Is multifactor authentication enabled, and does the user receive and successfully complete the MFA prompt?

    Is the Mac managed or registered through Intune, Company Portal, or another device-management solution?

    After clearing the Keychain entries, was the Mac restarted before the account was added again?

    If New Outlook is being used, does switching to Legacy Outlook change the behavior, or vice versa?

    In the meantime, kindly try the outlined steps of the AI-generate.

    Your provided information will help me assist you more promptly and efficiently.

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