0x800CCC0F
The connection to the server was interrupted
What it means
Outlook connected and then lost the session, often because a scanner or proxy closed it.
Common causes
- Antivirus email scanning
- A weak connection or VPN drop
- The server closed an idle connection
How to fix it
- Turn off email scanning in the antivirus and send a test message.
- Increase the server timeout in the account's advanced settings.
- Test the same account in webmail to rule out the server.
- Repair Office and restart Outlook.