An unknown error has occurred. Error Number: 0x800CCC0B

The error code 0x800CCC0B in Microsoft Outlook and Outlook Express typically indicates a problem related to the Simple Mail Transfer Protocol (SMTP). This error occurs when there is a conflict or issue with sending emails via the outgoing mail server. Here are several steps to troubleshoot and fix this error:

1. Check SMTP Server Settings

Ensure that your SMTP server settings are correct. Double-check the following details:

• SMTP server address
• Port number (commonly 25, 26, 465, or 587)
• Authentication requirements (username and password)
• SSL/TLS settings

2. Verify Your Internet Connection

Make sure you have a stable and active internet connection. Try browsing the internet or using another online service to verify connectivity.

3. Disable Firewall and Antivirus Temporarily

Firewalls or antivirus software can sometimes block the outgoing mail server connection. Temporarily disable these security measures to see if it resolves the issue. Remember to re-enable them after testing.

4. Increase Server Timeouts

If the server is slow to respond, increasing the server timeout setting can help:

1. Go to File > Account Settings > Account Settings.
2. Select the email account and click on Change.
3. Click on More Settings.
4. Navigate to the Advanced tab.
5. Increase the server timeout slider.

5. Repair Outlook Profile

A corrupted Outlook profile can cause this error. Create a new profile and test if it resolves the issue:

1. Go to Control Panel > Mail.
2. Click on Show Profiles.
3. Click on Add to create a new profile.
4. Configure your email account in the new profile.
5. Set the new profile as the default and test.

6. Check for Multiple Accounts

If you have multiple email accounts configured, make sure that the correct SMTP server settings are applied to each account.

7. Use Safe Mode

Start Outlook in safe mode to see if any add-ins are causing the issue:

1. Close Outlook.
2. Open the Run dialog (Win + R), type outlook.exe /safe, and press Enter.
3. If the error does not occur in safe mode, disable add-ins one by one to identify the culprit.

8. Update Outlook

Ensure you have the latest updates for Outlook. Microsoft often releases patches and updates that fix known issues.

9. Reinstall Outlook

If none of the above steps work, consider reinstalling Outlook. This can resolve any underlying software issues.

10. Contact Your Email Provider

If the problem persists, contact your email service provider. There might be an issue on their end or specific settings required for your account.

11. Check for ISP Blocking

Some Internet Service Providers (ISPs) block port 25 to reduce spam. If you are using port 25 for SMTP, try using port 26, 587 or 465 instead.

12. Verify the recipient email address

Another common reason for this error is that the recipient ID is invalid. Delete the mail in your outbox, create a new mail and check the recipient ID.

Following these steps should help you diagnose and fix the 0x800CCC0B error in Outlook. If the issue persists after trying these steps, more advanced troubleshooting or contacting professional support may be necessary.