0x800CCC0EOfficeHigh
Error 0x800CCC0E — Outlook Connection Failed | Microsoft Office Fix
Microsoft 365Office 2021Office 2019Office 2016
What Does 0x800CCC0E Mean?
Outlook cannot connect to the outgoing (SMTP) mail server. The connection to the server was interrupted or the server is unavailable.
Real-World Causes
- 1Incorrect SMTP server address or port number
- 2Firewall or antivirus blocking Outlook's connection
- 3ISP blocking port 25 for SMTP traffic
- 4SSL/TLS settings mismatch with mail server
Symptoms
- ⚠Cannot send emails from Outlook
- ⚠Error message appears when clicking Send/Receive
- ⚠Emails stuck in Outbox
- ⚠Timeout errors during send operation
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DIY Fix
Beginner-friendly steps you can try at home
- 1Verify SMTP server address and port (try port 587 with TLS)
- 2Temporarily disable antivirus/firewall to test connection
- 3Check internet connectivity and try a different network
- 4Verify account settings match your email provider's requirements
Advanced Fix
For experienced users and IT professionals
- 1Run Outlook in Safe Mode (outlook.exe /safe) to rule out add-in conflicts
- 2Recreate the Outlook email profile from scratch
- 3Check Windows Firewall exceptions for Outlook.exe
- 4Use telnet to test direct connectivity to the SMTP server and port
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Frequently Asked Questions
What ports should I use for SMTP?
Use port 587 with STARTTLS encryption (recommended) or port 465 with SSL. Port 25 is often blocked by ISPs. Check your email provider's documentation for the correct settings.
Why does this error appear suddenly?
Common causes include ISP changes, antivirus updates blocking Outlook, email provider changing server settings, or network firewall rule changes. Check for recent changes in your environment.
Related Error Codes
About the Author
Windows Troubleshooting Team
Verified against official Microsoft documentation and real-world diagnostic data. Error behavior confirmed across Windows 10, Windows 11, and Windows Server.