Outlook won't import gmail

Do not delete every MicrosoftOffice16_Data:OAUTH2 entry; remove only those whose full credential name contains tp_google_imap_Oauth2 for the affected Gmail account.

Identify and remove the Gmail credentials

1. Keep Outlook closed.
2. In Credential Manager → Windows Credentials → Generic Credentials, expand each entry beginning with: MicrosoftOffice16_Data:OAUTH2
3. Hover over the credential name to display its complete name.
4. Remove the entries whose full name contains: tp_google_imap_Oauth2 That text identifies Google IMAP OAuth credentials even though the visible label does not say “Gmail.” There are normally two credentials for each Gmail account.^1^
5. Reopen Outlook and select Sign in via browser. During Google authorization, select the permission allowing Microsoft apps and services to read, compose, send, and permanently delete Gmail messages.

If several Gmail accounts are configured

To avoid removing another Gmail account’s credentials, map the numeric portion of the credential to its Outlook identity:

1. Open Registry Editor only to inspect the entries; do not delete anything.
2. Navigate to:

Computer\HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Common\Identity\Identities

3. Find the identity subkey containing the affected Gmail address.
4. Match the number at the beginning of that identity key to the number in the full Credential Manager entry.
5. Remove only the matching tp_google_imap_Oauth2 credentials.

Microsoft documents this mapping specifically for selecting the affected account.^2^

If Outlook does not begin syncing after authentication, restart it once more. Removing these stored credentials forces a fresh sign-in; it does not remove the Gmail account from Outlook.^2^

References

1. Unable to add a Gmail account to classic Outlook | Microsoft Support
2. Users get errors 0x800CCC0E & 0x800CCC0F synchronizing Gmail and Yahoo accounts in classic Outlook | Microsoft Support