Error 0x800CCC0F in classic Outlook means the connection to the mail server was interrupted. For Outlook using IMAP/POP, use these steps:
- Fix the app password (IMAP/POP account)
- Sign in to the mail provider’s webmail.
- Go to Account Information → Security and create a new app password for Outlook.
- Open Outlook.
- Select File → under Account Information choose the affected IMAP/POP account.
- Select Account Settings → Server Settings.
- In IMAP Account Settings, paste the new app password into the Password box.
- Select Next, then Done.
- Test Send/Receive.
- If on Windows 10, disable TLS 1.3 (only if error persists)
- Close Outlook.
- Select Start, search for Regedit, and open Registry Editor.
- Browse to:
Computer\HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols
- Under Protocols, check if there is a TLS 1.3 key.
- If TLS 1.3 exists:
- Right‑click Protocols → Export to save a backup of the key.
- Delete the TLS 1.3 key and all its subkeys.
- Close Registry Editor.
- Restart Outlook; if still not syncing, restart Windows and test again.
If the issue is with a .pst data file (for example, frequent send/receive problems across accounts), run the Inbox Repair Tool as described in the Outlook data file repair article referenced below.
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