Fix Outlook Error 0x800ccc67: SMTP Server Response

Outlook error 0x800ccc67 usually appears when you try to send an email and the SMTP server rejects the connection or the message. The error text often reads “The server responded: 535 5.7.3 Authentication unsuccessful” or similar. This guide walks you through the most common fixes, from checking your SMTP port and authentication settings to clearing a stuck Outlook profile. No special tools are needed—just access to your email account settings and about 10 minutes.

What You’ll Need

Your email account’s SMTP server name and port (usually found in your email provider’s help pages or account settings)
Your email password (and an app password if you use two-factor authentication)
Access to Outlook’s account settings (File > Account Settings)
Administrator rights on your computer (only if you need to repair Office)

Step-by-Step

Check your SMTP settings in Outlook. Open Outlook, go to File > Account Settings > Account Settings. Select your email account and click Change. Look for Outgoing mail server (SMTP). Verify the server name matches your provider’s current SMTP address (for example, smtp.gmail.com for Gmail, smtp.office365.com for Microsoft 365). Also check the port number—common ones are 587 (STARTTLS), 465 (SSL), and 25 (often blocked).
Enable authentication for outgoing mail. In the same Internet Email Settings window, click More Settings > Outgoing Server tab. Check the box My outgoing server (SMTP) requires authentication. Choose Use same settings as my incoming mail server unless your provider says otherwise. Click OK.
Set the correct encryption and port. Go to More Settings > Advanced. Under Outgoing server (SMTP), set the port to 587 (recommended) and the encryption to TLS or STARTTLS. If your provider uses SSL, set port 465 and encryption to SSL. Click OK, then Next and Finish.
Re-enter your password. In the Change Account window, delete the password field and type it again. If you use two-factor authentication, you must create an app password from your email provider’s security settings and use that instead of your normal password. Click Next and let Outlook test the connection.
Repair the Outlook profile. If settings look correct but the error persists, close Outlook and open Control Panel > Mail (or search for “Mail” in Windows). Click Show Profiles, select your profile, and click Repair. Follow the prompts. This rebuilds the profile’s data files without deleting your emails.
Run the built-in Outlook repair tool. Go to Control Panel > Programs and Features, find Microsoft Office, right-click and choose Change (or Quick Repair). Select Quick Repair first—it takes a few minutes and fixes common file issues. If that doesn’t work, repeat with Online Repair (requires internet and may take longer).
Check if your ISP or firewall blocks port 25 or 465. Some internet service providers block SMTP ports other than 587. Try switching to port 587 with STARTTLS. Also temporarily disable your firewall or antivirus to test—if the email sends, add Outlook to the allowed list.
Create a new Outlook profile. If nothing else works, create a fresh profile: Control Panel > Mail > Show Profiles > Add. Give it a name, add your email account, and set it as the default. Then open Outlook with the new profile. This isolates any corruption in the old profile.

Common Mistakes

Using the wrong SMTP port. Many people leave port 25, which is often blocked by ISPs. Use 587 or 465 as your provider specifies.
Forgetting to enable SMTP authentication. If the “My outgoing server requires authentication” box is unchecked, the server rejects the login.
Using your regular password with two-factor authentication. When 2FA is on, you must generate an app-specific password in your email account settings.
Mixing up SSL and TLS. Using SSL on port 587 or TLS on port 465 causes a handshake failure. Match the port to the encryption method.
Leaving the old profile active. After repairing, if you still use the old corrupted profile, the error persists.

Tips

Always double-check your provider’s latest SMTP settings—they occasionally change.
If you use a VPN, disconnect it temporarily. Some VPNs interfere with SMTP connections.
Keep your Outlook and Windows updated. Microsoft regularly patches connection issues.
For Microsoft 365 accounts, make sure your mailbox isn’t over quota—this can cause sending failures.
Write down your working settings (server, port, encryption) in case you need to reconfigure later.

Troubleshooting

If the error persists after all steps:

Test the SMTP server manually. Open Command Prompt and type telnet smtp.yourprovider.com 587. If you get a blank screen or an error, the server is unreachable—check your internet connection or try a different network.
Try another email client. Configure the same account in a free client like Thunderbird or on your phone. If it works there, the problem is Outlook-specific; if not, the issue is with your account or network.
Check your email provider’s status page. Sometimes the provider has an outage. Wait a few hours and try again.
Clear the Outlook credential cache. In Windows, go to Control Panel > Credential Manager > Windows Credentials. Look for entries starting with Microsoft.Office or your email address, remove them, then restart Outlook and re-enter your password.
If you recently changed your email password, update it in every device. Outlook may be using a cached old password.

Frequently Asked Questions

What does error 0x800ccc67 mean?

It means Outlook could not authenticate with the outgoing SMTP server. The server rejected the login credentials, or the connection settings (port, encryption) are incorrect.

Will I lose my emails if I create a new profile?

No. Your emails are stored in a .pst or .ost file. When you create a new profile, you can attach the existing data file—Outlook will find it automatically if it’s in the default location.

Why does it work on my phone but not on Outlook?

Phone apps often use different default settings. Outlook on desktop may have an outdated SMTP port or missing authentication. Compare the settings in the phone app with those in Outlook.

Can I use port 25 to fix this error?

Port 25 is the standard SMTP port, but many ISPs block it to reduce spam. If your provider supports it, you can try, but 587 with STARTTLS is more reliable.

What is an app password and where do I get one?

An app password is a long, randomly generated password you create in your email account’s security settings. It lets Outlook bypass two-factor authentication. Look for “App passwords” or “App-specific passwords” in your provider’s security page.

How long does an Online Repair take?

It can take 15 to 30 minutes, depending on your internet speed and Office installation size. It will close all Office apps during the process.

General steps for current mainstream versions; menus can differ by device and version. See the disclaimer or report an error.

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