Outlook 2016 Sync Error

Reauthorize the Gmail account through Outlook’s Google browser sign-in and select Allow when Google requests mail access; this is the supported Outlook 2016 setup path and addresses Gmail authorization failures that can produce 0x800CCC0E. ^1^

Reauthorize Gmail

Before removing anything, copy or export any mail stored only under This computer only, local folders, or a PST file.

1. Verify that Gmail works in a web browser. This confirms that the Google account itself is accessible.
2. In Outlook, select File > Account Settings > Account Settings.
3. Select the Gmail account and choose Remove.
4. Restart Outlook.
5. Select File > Add Account.
6. Enter the complete Gmail address and select Connect.
7. Complete the Google browser sign-in.
8. On the Google permissions page, select Allow. Do not omit the permission allowing Microsoft apps and services to read, compose, send, and delete Gmail messages.
9. Finish setup, restart Outlook, and run Send/Receive All Folders.

Microsoft documents missing Google mail consent as a cause of Gmail IMAP setup and synchronization failures. ^2^

If Outlook does not prompt you to sign in

If File > Office Account shows a Microsoft 365 subscription rather than perpetual Outlook 2016, clear the stale Google OAuth credentials. Microsoft’s documented 0x800CCC0E issue and this workaround apply to Outlook for Microsoft 365. ^3^

1. Close Outlook.
2. Open Windows Credential Manager.
3. Select Windows Credentials.
4. Under Generic Credentials, expand entries beginning with MicrosoftOffice16_Data:OAUTH2.
5. Identify entries whose full names contain tp_google_imap_Oauth2.
6. Remove all matching entries for the affected Gmail account—normally two or four.
7. Start Outlook and complete the Google sign-in.
8. Restart Outlook once more if synchronization does not begin immediately.

Removing these credentials signs the account out; it does not remove the Outlook account.

If that still does not trigger sign-in, the same Microsoft article provides a registry fallback. Back up the registry first because deleting the wrong key can affect other Office identities.

1. Close Outlook.
2. Press Windows+R, enter regedit, and select OK.
3. Go to:

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

4. Inspect the subkeys until the affected Gmail address is found.
5. Delete only that Gmail identity subkey.
6. Restart Outlook and sign in again.

If only “Sent Mail” continues to fail

In Gmail on the web:

1. Open Settings > See all settings > Labels.
2. Find Sent Mail.
3. Ensure Show in IMAP is enabled.
4. Also verify Inbox, Trash, and All Mail are shown in IMAP.
5. Restart Outlook and allow up to 15 minutes for synchronization to refresh.

Microsoft specifically requires Gmail folders such as Sent Mail to be exposed through IMAP for Outlook to access them. ^4^

If the account was configured manually, its incoming settings should be imap.gmail.com, SSL enabled, port 993; outgoing settings should use smtp.gmail.com, authentication enabled, and SSL port 465 or TLS/STARTTLS port 587. ^4^

Outlook 2016 reached end of support on October 14, 2025, so it no longer receives security updates, bug fixes, or technical support. Plan to move to a supported Outlook version if reauthorization does not resolve the issue. ^5^

References

1. [Classic Outlook](https://support.microsoft.com/outlook/getstarted/add-a-gmail-account-to-outlook-for-windows)
2. Unable to add a Gmail account to classic Outlook | Microsoft Support
3. Users get errors 0x800CCC0E & 0x800CCC0F synchronizing Gmail and Yahoo accounts in classic Outlook | Microsoft Support
4. Fix problems connecting your Google account to the Microsoft Cloud | Microsoft Support
5. Products reaching end of support on October 14, 2025