How do I resolve the oauth popup issue when trying to access mail from desktop Outlook 365 Classic?

Question

How do I resolve the oauth popup issue when trying to access mail from desktop Outlook 365 Classic?

David Thelen 5

Tying to acccess my yahoo mail account from desktop Outlook 365 Classic. Got oauth agreement pop up from outlook. I clicked on Agree and it did nothing. I clicked on ignore and same thing. It was not allowing me to download my new emails from the Yahoo mail server. I have taken the following steps to resolve: Clear cookies and cache, reboot everything, create backup file and delete the yahoo mail account from outlook, run online repair of office 365, cleared cached Yahoo credentials and attempted reinstall (fails to reinstall after closing pop up window). Run outlook in safe mode and attempt reinstall (fails again). Trying a passkey also does not work.

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Answer 1

Kal-D 3,460 Microsoft External Staff Moderator

Dear David Thelen,

Thank you for posting on the Microsoft Q&A forum.

The issue with the unresponsive "Agree" button is typically caused by corrupted authentication tokens. The path to resolution involves a deep reset of these tokens.

Please follow these steps in sequence.

Step 1: Prepare Browser and Yahoo Account

The OAuth pop-up uses Microsoft Edge in the background, and its extensions can interfere.

Open Microsoft Edge.
Go to Settings > Extensions and temporarily disable all extensions, especially ad-blockers and privacy tools.
Now, log in to your Yahoo Mail account via a web browser.
Navigate to your Account Security settings, find "Connected Apps" or "Third-Party Access," and revoke access for any entry related to Microsoft Outlook.

Step 2: Deep Credential & Profile Reset

Disclaimer: Profile & Data Consideration Deleting an Outlook profile will remove its configuration. While emails on the server (IMAP) are safe, any local data stored only in that profile (e.g., "On This Computer Only" contacts or calendar entries) will be lost. Your backup (.pst) file protects this data.

Close Outlook completely.
Delete the Outlook Profile:
- Press Windows Key + R, type outlook.exe /profiles, and press Enter.
- Select the profile containing your Yahoo account and click Remove.
Clear Windows Credentials:
- Press Windows Key + R, type control keymgr.dll, and press Enter.
- Go to Windows Credentials.
- Caution: Review the list carefully. Remove only entries clearly related to Yahoo, Office, or OAuth2. Avoid deleting other system credentials.
Re-add Your Account:
- Open Outlook. It will guide you to create a new profile.
- Add your Yahoo account. The OAuth process should now initiate cleanly.

Step 3: Guaranteed Fallback - Use a Yahoo App Password

If the OAuth pop-up continues to fail after the complete reset above, the most reliable workaround is to bypass it using an App Password. This is a common and stable solution for persistent OAuth compatibility issues.

Log in to your Yahoo Account Security page online.
Enable Two-Factor Authentication (a requirement for generating an App Password).
Generate a unique 16-digit App Password.
In Outlook, when prompted for the password for your Yahoo account, use this App Password instead of your regular account password.

Please execute Steps 1 and 2 together. This combination resolves the majority of these authentication blocks. If the issue persists, please proceed with Step 3.

Please let me know if you encounter any trouble with these steps.

I'm looking forward to hearing from you.

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David Thelen 5 Reputation points

2025-11-03T18:05:15.6866667+00:00

Good Morning. Completed step 1. Step 2- subsection 2- there is no profile containing my yahoo mail account as I had previously backed up and deleted that mail account from my profile. Completed subsection 3. Subsection 4- same result. Pop up does not go away after hitting either accept or later. Account not added. Step 3- 2 factor enabled and app password created. When trying to create new yahoo mail account it asks for username and goes straight to the pop up without prompting for password. Then same result.
David Thelen 5 Reputation points

2025-11-03T18:29:39.1966667+00:00

Update- logged out of all online access to yahoo mail and restarted computer. When I went to add profile it prompted for 2 factor authentication and pw. When I tried the new app pw I created it failed. When I tried my yahoo mail password it went through BUT got the same unresolvable oauth pop up.
Kal-D 3,460 Reputation points Microsoft External Staff Moderator

2025-11-03T21:48:40.8433333+00:00
Hi David Thelen,

Thank you for the detailed update. This clarifies the situation perfectly. The fact that the OAuth pop-up appears instead of a password prompt, even with a new profile, confirms that Outlook is hard-locked into using the broken OAuth flow. The system is not giving you a chance to use the App Password.

We need to force Outlook to bypass the OAuth pop-up entirely and present the classic password prompt.

Force Manual Setup via Outlook's Options

Since the OAuth pop-up is blocking everything, we need to access the manual configuration from inside Outlook itself.

Open Outlook. If it starts the "Add Account" wizard automatically, click the "X" to cancel and close it. You need to get to the main Outlook screen.

Once in the main Outlook window, go to: File -> Account Settings -> Manage Profiles

Click Show Profiles....

Select your current profile and click Properties.

Alternatively, if you have multiple, ensure the correct one is set as default.

Now, click the Email Accounts... button. This opens the classic account management window.

Here, click the New... button to add a new account.

This is the critical step: In the "Add Account" dialog box that appears, immediately click the option at the bottom that says "Manual setup or additional server types" and then click Next. (This is the bypass we need. It will not trigger the OAuth pop-up.)

On the next screen, choose POP or IMAP and click Next.

You will now see the manual configuration screen. Fill it out as follows, using your 16-digit App Password:

Your Name: Your Name

Email Address: ******@yahoo.com

Account Type: IMAP

Incoming mail server: imap.mail.yahoo.com

Outgoing mail server (SMTP): smtp.mail.yahoo.com

User Name: ******@yahoo.com

Password: [Your 16-digit Yahoo App Password] <-- This is the key.

Require logon using Secure Password Authentication (SPA): Leave this UNCHECKED.

Before clicking Next, click the More Settings... button.

Go to the Outgoing Server tab: Check "My outgoing server (SMTP) requires authentication" and select "Use same settings as my incoming mail server".

Go to the Advanced tab:

Incoming server (IMAP): 993

Use the following type of encrypted connection: SSL/TLS

Outgoing server (SMTP): 587

Use the following type of encrypted connection: STARTTLS

Click OK

Now click Next. Outlook will test the account settings. With the correct App Password, this should finally succeed.

This method gives you full control and completely bypasses the broken automated OAuth process.

Please try these steps and let me know if it works for you.

I'm looking forward to hearing from you.
David Thelen 5 Reputation points

2025-11-04T02:07:07.78+00:00

Hi Kal-D. I followed your instructions to the letter and was able to successfully add the yahoo mail account back into the profile HOWEVER when trying to send and receive new emails Outlook prompted for a password. It did not recognize the app password but it did recognize the old password I used before. It then texted my phone with an authentication code which I entered into Outlook and then the dreaded oauth pop up came up and I could go no further. Interestingly enough I did get an error message as follows:

20:55:28 Synchronizer Version 16.0.19328.20010

20:55:28 Synchronizing Mailbox '******@yahoo.com'

20:55:28 Synchronizing Hierarchy

20:57:55 Error in folder 'Inbox'

20:57:55 [800CCC0E-0-0-733]

20:57:55 Terminated in error

20:57:55 [800CCC0E-0-0-733]
David Thelen 5 Reputation points

2025-11-04T03:01:14.7466667+00:00

Update: the test message sent by outlook ended up going to the yahoo mail server but outlook will not pull down any messages on the server because of the dreaded oauth pop up. I took some additional steps to resolve. Even though I updated Microsoft OS there was another update available for Microsoft 11- V25H2. I downloaded and installed that and rebooted the computer. I then went back and followed your initial instructions making sure all add ons were turned off. However I was not able to find this section in yahoo mail- Navigate to your Account Security settings, find "Connected Apps" or "Third-Party Access," and revoke access for any entry related to Microsoft Outlook. I also cleared out the Windows credentials.
Kal-D 3,460 Reputation points Microsoft External Staff Moderator

2025-11-04T15:47:35.11+00:00
Hi David Thelen,

Thank you for the detailed update and your incredible persistence. The key clue is that it accepted your old password and then demanded the OAuth pop-up, which means Outlook is still stubbornly trying to use the modern authentication method despite our efforts to force the older, manual one.

We need to take two decisive actions: force-disable modern authentication at a system level and then ensure the manual configuration is perfectly locked in.

Step 1: Force-Outlook to Stop Using OAuth (Registry Edit)

This is the most critical step. We will tell Windows/Office to completely disable the modern authentication library that is causing the pop-up.

Disclaimer: Advanced System Change

This involves editing the Windows Registry. Incorrect changes can cause system instability.

Please back up your registry first. You can do this by opening the Registry Editor (regedit) and going to File > Export to save a copy.

Proceed with caution and follow the steps exactly.

Close Outlook completely.

Press Windows Key + R, type regedit, and press Enter.

Navigate to the following folder path in the left-hand pane. If the Identity folder does not exist, you will need to create it.

HKEY_CURRENT_USER\SOFTWARE\Microsoft\Office\16.0\Common\Identity

(The 16.0 is for the current Office 365; it is the correct version.)

In the Identity folder, right-click in the right-hand pane and select New > DWORD (32-bit) Value.

Name this new value EnableADAL.

Double-click on EnableADAL and set its Value data to 0.

Click OK and close the Registry Editor.

This disables the modern authentication stack system-wide for Office.

Step 2: Re-Create the Yahoo Account with the App Password

Now, we must delete and re-add the Yahoo account to ensure it picks up the new setting. The previous configuration is "tainted."

Go to File > Account Settings > Account Settings.

Select your Yahoo account and click Remove. Confirm the deletion.

Now, follow the manual setup process from our last instructions again to re-add the account:

Go to File > Account Settings > Manage Profiles > Show Profiles... > [Select Profile] > Properties > Email Accounts... > New...

Select "Manual setup or additional server types".

Choose POP or IMAP.

Enter all the server settings again, making absolutely certain to use the 16-digit App Password in the password field.

In More Settings > Advanced, verify the ports are correct (IMAP: 993/SSL, SMTP: 587/STARTTLS).

Step 3: Locate the Yahoo "Connected Apps" Page

This is crucial to ensure Yahoo isn't sending a mixed signal. The location can be tricky.

Log into your Yahoo mail in a web browser.

Click on your profile picture or initials in the top-right corner.

Select Account Info or Yahoo Account settings.

On the left-hand menu, click Account Security.

Scroll down until you find a section named "Apps and sessions" or similar.

Look for a subsection like "Connected apps" or "Manage apps". Here you should see and can revoke access for "Microsoft Outlook".

After completing all three steps, restart your computer one final time to clear all caches, then test Outlook. By disabling ADAL, we are forcing Outlook to fall back to the basic authentication method, which should honor the manual IMAP setup and your App Password without any pop-ups.
David Thelen 5 Reputation points

2025-11-05T18:34:53.5666667+00:00

Hi there. Can you please keep this ticket open until I can work on the new recommendations and report back to you? I have not had a moment to work on this yet?
Kal-D 3,460 Reputation points Microsoft External Staff Moderator

2025-11-11T15:43:55.4366667+00:00

Hi David Thelen,

It has been a while since your last approach.

May I know if you have any updates from your end.

I am looking forward to your response.
David Thelen 5 Reputation points

2025-11-11T20:30:25.24+00:00

Hi there. I need a little more time to try your last solution.
Kal-D 3,460 Reputation points Microsoft External Staff Moderator

2025-11-12T20:53:39.0666667+00:00

Hi David Thelen,

If you're still encountering any problems or have run into new challenges, please let me know which steps you're currently stuck on and happy to provide further help whenever you need it.
David Thelen 5 Reputation points

2025-11-21T03:22:51.3766667+00:00

Hey Cal. I finally had some time to do all the steps you provided to resolve this issue. It took about 20 minutes. Bad news is that it did not work and the oauth popup took over once more. I'm not ready to give up just yet. What else can be done?
David Thelen 5 Reputation points

2025-12-06T05:31:33.8433333+00:00

Hi Cal. I still need help with this issue per my previous post.

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How do I resolve the oauth popup issue when trying to access mail from desktop Outlook 365 Classic?

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