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Classic Outlook - Windows

Outlook modern authentication not working?

If classic Outlook keeps prompting you for a password and never accepts it, the cause is almost always that basic authentication has been retired - so an old manual setup that relied on it can no longer sign in. The fix is to update Office so it uses modern OAuth 2.0, clear the stale cached credentials Windows is holding, confirm the account allows modern auth, and use an app password where your organisation permits one. Here's exactly how - or we'll fix it remotely in minutes.

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By the 365 Techies team · Reviewed 10 October 2026

Why it happens

Why Outlook keeps prompting for your password

For years, email apps signed in with "basic authentication" - your username and password sent straight to the mail server. Microsoft has now retired basic authentication for both personal Outlook.com accounts (from September 2024, covering Outlook.com, Hotmail, Live and MSN) and for business Exchange Online mailboxes. Anything still trying to sign in the old way gets refused, and Outlook responds by asking for the password again... and again.

So a repeating password prompt that never sticks is the classic symptom of an old manual setup, or an out-of-date Office install, still trying to use basic auth. The answer is to move that account onto modern authentication (OAuth 2.0), which signs in through a proper Microsoft or provider login window instead of quietly passing your password to the server.

Two phrasings, one problem: whether you're seeing "modern authentication not working" or Outlook simply "keeps prompting for a password", the fix below covers both.

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We do not support Outlook on Apple Macs, iPads or iPhones. Apple does not allow our remote-support tool to take control of an iPad or iPhone (an Apple restriction), and our remote support covers Windows PCs only. On an Apple device, Microsoft’s own Outlook help is the place to start.

// FIX IT WITH ME · STEP BY STEP

Fix it with me, one step at a time

The steps from this guide, one at a time, in the order that fixes the most cases fastest. Tell it what happened and it shows the next step. Nothing here leaves your device.Last reviewed 10 October 2026

Checking which Windows you have…STEP 1 OF 5
  1. 01Update Office to the latest build

    In any Office app go to File, Account, Update Options, Update Now, then restart, so Office uses modern OAuth 2.0 instead of the retired basic authentication.

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The fix

How to fix modern authentication in classic Outlook

  1. Update Office to the latest build. Open any Office app, go to File, Account, Update Options, then Update Now. A current Office build supports OAuth 2.0 sign-in, but Microsoft says Outlook 2013, Outlook 2016 MSI and Outlook 2019 LTSC cannot use it for Outlook.com or Hotmail, however up to date they are. Restart after updating.
  2. Clear the cached Office logins in Credential Manager. Close Outlook completely, then open Control Panel, User Accounts, Credential Manager, Windows Credentials. Remove every entry that begins with MicrosoftOffice16_Data:SSPI (and any older MicrosoftOffice15_Data entries) as well as anything referencing your Outlook or Microsoft 365 account. These are the stale saved passwords behind many repeat prompts. Restart the PC, reopen Outlook, and sign in when the proper login window appears.
  3. Confirm the account allows modern auth. Modern authentication needs to be enabled on the mailbox or tenant. For a work or business account, your Microsoft 365 administrator can confirm it's switched on - if basic auth was all that ever worked, the account may need modern auth enabled before Outlook can connect.
  4. Use an app password only where it's still allowed. If the account uses two-step verification and your organisation still permits app passwords, generate one in the account's security settings and paste it into Outlook in place of your normal password. Note: Microsoft has removed app passwords for personal Outlook.com/Hotmail accounts, so for those you must sign in through the modern login window instead - app passwords remain relevant mainly for some organisation and third-party (Gmail/Yahoo) accounts.
  5. Recreate the profile if it still prompts. If the account was originally set up manually for basic auth, the cleanest fix is to remove it and add it again so Outlook builds it with modern auth from the start. Your mail re-downloads from the server, but back up any POP-only mail first, since POP messages may exist only on your PC.

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// GOOD QUESTIONS

Frequently asked

What is modern authentication and why has basic auth stopped working?

Modern authentication (OAuth 2.0) signs you in through a secure Microsoft or provider login window and supports multi-factor authentication, instead of passing your password straight to the mail server like the old "basic authentication" did. Microsoft has retired basic auth for security reasons - for personal Outlook.com, Hotmail and Live accounts this happened in September 2024, and for business Exchange Online mailboxes it has already been retired too. Older setups that relied on it now get refused, which shows up as endless password prompts.

Which Credential Manager entries should I remove?

Close Outlook first, then in Control Panel, Credential Manager, Windows Credentials, remove entries starting with MicrosoftOffice16_Data:SSPI (and older MicrosoftOffice15_Data entries), plus anything referencing your Outlook or Microsoft 365 email. These hold outdated saved passwords. Restart, reopen Outlook, and let the proper sign-in window appear so it stores a fresh, modern login.

Do I still need an app password?

It depends on the account. Microsoft has removed app passwords for personal Outlook.com, Hotmail, Live and MSN accounts - for those you sign in through the modern login window. App passwords are still used for some organisation accounts that allow them and for third-party providers like Gmail and Yahoo when two-step verification is on. If your account qualifies, generate one in its security settings and paste it into Outlook instead of your normal password.

Is it safe to clear cached credentials - will I lose emails?

Yes, it's safe. Clearing cached credentials only removes stored passwords, not your email. Your mail stays on the server and re-downloads when you sign back in. The one exception is POP accounts, where messages may exist only on your PC - so if you have a POP account, back up its data file before making bigger changes like recreating the profile.

I'm not an admin - can I still fix this myself?

Often yes. Updating Office and clearing Credential Manager are things you can do on your own PC. But if modern authentication needs enabling on a business mailbox, or a security policy is blocking the sign-in, that part needs a Microsoft 365 administrator. If you're not sure where the block is, we can identify it quickly for you.

Can 365 Techies fix these password prompts remotely?

Yes. We're a Microsoft Partner based in Bournemouth. We'll phone you first, connect with your permission so you can watch the whole session, update Office, clear the stale credentials and get modern auth working, then disconnect once it's sorted - usually within minutes. Call 01202 775566.

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