Gmail account cannot be added to Classic Outlook — "This email address has already been added"

Question

As of March 18, 2026, my Gmail account stopped working in Classic Outlook (2021/2024) on Windows. When trying to re-add the account I get the error message "This email address has already been added", despite the account being removed.

Steps already taken without success:

• Updated Outlook to the latest version
• Removed the account from Outlook and attempted to re-add it
• Cleared all related entries in Credential Manager
• Searched the registry (regedit) for the Gmail address and removed all matches
• Created a new Outlook profile
• Uninstalled New Outlook
• Attempted to add the account manually via IMAP
• Removed a remaining Google Calendar entry in Outlook
• Checked Windows Settings under Accounts — the account is not listed there

None of the above has resolved the issue. Outlook appears to retain a reference to the Gmail account in a location that cannot be reached manually.

System information:

• Outlook version: Classic Outlook 2021/2024
• OS: Windows 11

Please help me identify and remove the remaining account reference so that I can re-add my Gmail account.As of March 18, 2026, my Gmail account stopped working in Classic Outlook (2021/2024) on Windows. When trying to re-add the account I get the error message "This email address has already been added", despite the account being removed.

Steps already taken without success:

• Updated Outlook to the latest version
• Removed the account from Outlook and attempted to re-add it
• Cleared all related entries in Credential Manager
• Searched the registry (regedit) for the Gmail address and removed all matches
• Created a new Outlook profile
• Uninstalled New Outlook
• Attempted to add the account manually via IMAP
• Removed a remaining Google Calendar entry in Outlook
• Checked Windows Settings under Accounts — the account is not listed there

None of the above has resolved the issue. Outlook appears to retain a reference to the Gmail account in a location that cannot be reached manually.

System information:

• Outlook version: Classic Outlook 2021/2024
• OS: Windows 11

Please help me identify and remove the remaining account reference so that I can re-add my Gmail account.

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Answer 1

If the issue persists, you can try repairing your account.

In Outlook, go to File > Account Settings, select your email account, then click the Repair button.

If the issue continues, you may want to use the Outlook web version temporarily while Microsoft is fixing the issue.

Answer 2

Hi,

Several users have recently reported experiencing this issue. The Microsoft team is currently aware of the problem and is actively investigating the cause. While a permanent fix has not yet been released, Microsoft has provided a temporary workaround that may help resolve the issue in the meantime. You can find the details of the current workaround here:

https://support.microsoft.com/office/users-get-errors-0x800ccc0e-0x800ccc0f-synchronizing-gmail-and-yahoo-accounts-in-classic-outlook-e5a7b684-7c5c-4848-ab2d-d48291451f67

Answer 3

Followed exact steps and issue persists

Answer 4

The remaining reference is almost certainly the stored Google OAuth/IMAP identity that Outlook is still holding onto. Microsoft documents a specific cleanup path for classic Outlook + Gmail issues that goes beyond just deleting obvious credentials and registry hits.

Follow this exact sequence, including the Google-side cleanup, then re-add the account using the browser sign-in flow.

1. Remove Outlook’s access in Google
   1. Close Outlook completely.
   2. Sign in to the affected Google account at https://www.google.com.
   3. Select the profile picture → Manage your Google Account.
   4. In the left menu, select Security.
   5. Scroll to Your connections to third-party apps & services and select Microsoft apps & services.
   6. Under Microsoft apps & services has some access to your Google Account, select See details.
   7. Under Access you've given to Microsoft apps & services, select Remove all access.
   8. Confirm.
2. Remove the specific Google IMAP OAuth credentials from Credential Manager
   1. From the Windows Start menu, open Credential Manager (in Windows 11 this is under Control Panel → Credential Manager).
   2. Select Windows Credentials.
   3. Under Generic Credentials, locate entries starting with MicrosoftOffice16_Data:OAUTH2.
   4. Expand each one and hover over the name until the full string shows, including tp_google_imap_Oauth2. These are the Gmail IMAP credentials.
   5. Remove each credential that contains MicrosoftOffice16_Data:OAUTH2 and tp_google_imap_Oauth2. There are two such credentials per Gmail account; remove both for the affected account.
   6. If multiple Gmail accounts exist and only one should be removed, map credentials to identities using the registry key below before deleting:
      • Open Registry Editor and paste this path in the address bar:
        • Computer\HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Common\Identity\Identities
      • Use the numeric prefix in each identity key to match the corresponding credential in Credential Manager, then remove only those two matching MicrosoftOffice16_Data:OAUTH2 entries.
3. Clean up the Outlook identity reference (if not already done this way)
   1. In Registry Editor, go to:
      • Computer\HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Common\Identity\Identities
   2. Identify the subkey that corresponds to the affected Gmail identity (the numeric part at the beginning matches the number in the Credential Manager entries above).
   3. Delete only that identity subkey.
4. Ensure Outlook has the Gmail fix (for sign-in issues)
   • The Gmail sign-in problem in classic Outlook has been fixed in specific builds. Make sure Outlook is on a build that includes the fix (for Outlook for Microsoft 365 this is Version 2404 / Build 17531.10000 or later; for perpetual versions ensure the latest updates are installed).
   • After updating, restart Outlook.
5. Re-add the Gmail account using the browser sign-in flow
   1. Start Outlook with the profile where the Gmail account should be added.
   2. If the account was still present but not syncing, use the Sign in via browser bar in Outlook and complete sign-in.
   3. If the account was removed from the profile:
      • Go to File → Add account.
      • Enter the Gmail address.
      • When the Google sign-in page opens in the browser, sign in and, importantly, check the box for Microsoft apps & services when granting access.
   4. Finish the wizard and let Outlook complete the setup.

After these steps, the hidden identity and OAuth references that cause “This email address has already been added” should be removed, allowing the Gmail account to be added again in Classic Outlook.

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References:

• Unable to add a Gmail account to classic Outlook
• Unable to sign in or add a Gmail account to classic Outlook
• gmail accounts no longer working in outlook classic - Microsoft Q&A
• search for solutions another user has found - Microsoft Q&A