You see the error 0x800CCC79 when Outlook cannot send an email. This error means the recipient’s email address was rejected by your outgoing mail server. The server’s security or configuration rules blocked the address. This article explains why this rejection happens and provides steps to resolve it.
Key Takeaways: Fixing SMTP Address Rejection Error 0x800CCC79
- Verify Recipient Address: Check for typos in the email address and confirm it with the recipient.
- File > Account Settings > Server Settings: Ensure your SMTP server name and port number are correct for your email provider.
- Outgoing Server (SMTP) > Properties > Advanced: Adjust the SMTP port to 587 or 465 and enable SSL/TLS encryption if your provider requires it.
Why Your SMTP Server Rejects the Recipient Address
Error 0x800CCC79 is an SMTP protocol error. Your outgoing mail server performs checks on the recipient address before attempting delivery. If the address fails these checks, the server rejects it immediately and sends this error code back to Outlook. The rejection happens on your side, not at the recipient’s server.
Common reasons include a simple typo in the email address. The server’s anti-spam filters may also block addresses from certain domains known for spam. Sometimes, the server configuration requires specific security settings, like using a non-standard SMTP port or encryption, which are missing in your Outlook setup.
How Server-Side Rules Trigger the Error
Your email provider or company IT department sets rules on the SMTP server. These rules can block addresses containing specific words, coming from free webmail domains, or not matching internal directory formats. The rejection is instant, so you get the error as soon as you click Send.
Steps to Resolve the SMTP Recipient Rejection Error
Follow these steps in order. Start by checking the recipient address and then verify your Outlook SMTP configuration.
- Check the recipient’s email address for typos
Open the unsent message from your Outbox. Carefully examine the email address in the To, Cc, and Bcc fields. Look for misspellings, missing dots, or incorrect domain extensions like .con instead of .com. If possible, confirm the correct address with the recipient. - Verify your SMTP server settings in Outlook
Go to File > Account Settings > Account Settings. Select your email account and click Change. On the Change Account window, click More Settings. Go to the Outgoing Server tab. Ensure the “My outgoing server (SMTP) requires authentication” box is checked and set to “Use same settings as my incoming mail server.” - Configure the correct SMTP port and encryption
In the More Settings window, go to the Advanced tab. Find the Outgoing server (SMTP) section. The default port is 25. Many modern providers use port 587 with STARTTLS or port 465 with SSL. Change the port number based on your provider’s instructions. Below the port, set the encryption to SSL/TLS or STARTTLS as required. Click OK. - Test the corrected settings
Back on the Change Account screen, click Next. Outlook will test your account settings. If the test passes, click Close and then Finish. Try sending the email again. If the test fails, note the error for the next step. - Contact your email provider or IT support
If the error persists, the block is likely a server-side rule. Contact your email service provider’s support or your company’s IT helpdesk. Provide them with the exact recipient address and the error code 0x800CCC79. They can check their SMTP server logs and security policies.
If the Error Persists After Configuration Changes
Sometimes the standard fixes do not work because of other underlying issues. Here are specific scenarios and their solutions.
Outlook Still Shows Error 0x800CCC79 After Correcting Settings
Close Outlook completely and restart it. A restart forces Outlook to use the new SMTP settings. If that fails, create a new Outlook profile. Go to Control Panel > Mail > Show Profiles > Add. Set up your email account with the correct SMTP details from the start. This eliminates corruption in the old profile.
The Recipient Address is Correct But Blocked by Policy
Your organization may block emails to certain external domains for security. Try sending the email to a different address, like a personal Gmail account, to test. If that works, the original recipient’s domain is blocked. You must request an exception from your IT administrator, who can whitelist the domain.
Error Occurs Only with Specific Recipients or Large Attachments
Some servers reject messages if the total size, including attachments, exceeds a limit. Remove large attachments and try sending a plain text email. If it sends, the issue is the message size. Compress files or use a cloud storage link instead. Also, check if the recipient’s address has a plus sign (+) or unusual characters that some filters block.
Common SMTP Configuration Ports and Encryption Methods
| Item | Port 587 with STARTTLS | Port 465 with SSL/TLS | Port 25 (Unencrypted/Deprecated) |
|---|---|---|---|
| Primary Use | Default for most modern email providers | Legacy SMTPS method | Original SMTP port, often blocked by ISPs |
| Encryption | Starts unencrypted, negotiates TLS | Full SSL/TLS encryption from connection start | No encryption, plain text |
| Outlook Setting | Encryption: STARTTLS | Encryption: SSL/TLS | Encryption: None |
| Reliability | High, works on most networks | High, but less commonly supported now | Low, frequently blocked for anti-spam |
You can now diagnose and fix the recipient rejection error in Outlook. Start by verifying the email address and updating your SMTP server port. For persistent blocks, contact your email provider to check server-side filters. As an advanced tip, use the Test Account Settings feature in Outlook after any change to get immediate feedback on your configuration.