Troubleshooting Outlook Error 0x800CCC79

Error 0x800CCC79 is a delivery failure notification accompanied by the message “Relay access denied.” This occurs when your email client (such as Microsoft Outlook or Windows Live Mail) tries to send an email through the mybox server without proving who you are first.

In the early days of the internet, mail servers allowed anyone to send mail through them. Today, to prevent spam, mybox requires “SMTP Authentication”-essentially a digital ID check-before it will “relay” your message to the recipient’s inbox.

Common Causes

1. Missing Authentication: The “My outgoing server (SMTP) requires authentication” box is unchecked in your Outlook settings.
2. Incorrect Credentials: Outlook is trying to log in to the outgoing server with a different username or password than the one used for your incoming mail.
3. Typo in Email Address: Occasionally, a malformed recipient address can trigger a relay error if the server cannot determine where to send the message.

Distinction Block

Login vs. Relay

Login is when you connect to imap.mybox.com to read your mail. Relay is when you ask smtp.mybox.com to send your mail to someone else. Error 0x800CCC79 means the server let you log in to read, but blocked you from sending because you didn’t provide your credentials a second time for the “relay” process.

How to Resolve

To fix error 0x800CCC79, you must enable SMTP authentication in your email account settings:

1. Enable Outgoing Authentication

• Open Outlook and go to File > Account Settings > Account Settings.
• Select your mybox email account and click Change.
• Click the More Settings button.
• Go to the Outgoing Server tab.
• Check the box: “My outgoing server (SMTP) requires authentication”.
• Ensure “Use same settings as my incoming mail server” is selected.

2. Verify Port and Encryption While in the More Settings window, switch to the Advanced tab and ensure you are using the correct mybox infrastructure:

• Outgoing Server (SMTP): smtp.mybox.com
• Port: 587
• Encryption: STARTTLS or TLS

Practical Implications

• Immediate Resolution: Once you check the authentication box, the “Relay access denied” error should disappear instantly. You can test this by clicking “Test Account Settings” in Outlook.
• Security: Using authentication ensures that no one else can “spoof” your email address using the mybox servers. It protects your sender reputation and ensures your mail doesn’t end up in your recipients’ spam folders.
• Mobile Devices: If you use the same email on a smartphone, ensure the “Outgoing Mail Server” settings on your phone also have “Authentication” set to Password.

Summary

Error 0x800CCC79 is a simple “ID check” failure. By ensuring that your client is configured to provide your username and password when sending mail to smtp.mybox.com, you fulfill the security requirements of the mybox infrastructure and ensure reliable mail delivery.