How to Fix Outlook Error Code 0x800ccc78?

Summary: If you're experiencing the Outlook error 0x800ccc78, follow this guide to know the common reasons that can trigger this error and some simple solutions to fix it. It also mentions an advanced PST repair tool that can help fix the error if the cause is corruption in the PST file.

The error 0x800ccc78 is one of the Outlook errors that appears when you’re trying to send or receive new emails and meeting invites. It also prevents making any other changes to Outlook, such as moving or deleting messages from the mail folders.

If you try to send a new email or manually update folders to receive new emails, Microsoft Outlook fails to operate and displays the following error message:

“Sending’ reported error (0X800CCC78): Cannot send the message. Verify the email address in your account properties. The server responded: 550 access denied-Invalid Helo name(See RFC2821 4.1. 1.1)”.

The error is often accompanied by the following issues:

1. Inability to send or receive new messages or emails
2. Outlook freezes, stops responding, or crashes frequently
3. Slow Outlook performance
4. Outlook takes longer to load or display search results
5. Users may fail to access their calendar or other Outlook features

In this guide, you will learn the reasons that can trigger the 0x800ccc78 error in Outlook and the solutions to troubleshoot and resolve it effectively. 

Reasons for Outlook Error 0x800ccc78

There could be several potential causes that can trigger the error 0x800ccc78 in Outlook. These include:

1. Incorrect or outdated email settings
2. Authenticity issues due to network connection or expired password
3. POP (SMTP) mail server-related issues
4. Outdated Outlook
5. Conflict with other programs, such as antivirus
6. Damaged or corrupt Outlook PST file
7. Large or oversized PST file
8. Corrupt Outlook profile
9. Faulty or incompatible add-ins

Solutions to Troubleshoot and Resolve the Error 0x800ccc78 in Outlook

Below are some solutions that you can apply to troubleshoot and resolve the Outlook error 0x800ccc78.

Solution 1: Check the Network Connection

An unstable or poor network connection on the client machine or server can prevent Outlook from communicating or making a stable connection with the mail server, leading to the error 0x800ccc78. Therefore, it is important to have a stable network connection. To check and troubleshoot the network issues, do the following:

• Try connecting to a different Wi-Fi (wireless) or wired network
• Check and reconnect the Ethernet cable
• Restart the modem and/or router
• Disable VPN if there’s any
• Change DNS to 8.8.8.8 and 8.8.4.4
• Open a web browser window on your system and visit any site to check whether the internet is working
• Try to log in to the webmail version (webmail.yourdomain.com or similar) and ensure that the server is online and available

Solution 2: Double-Check Email Settings

It’s important to verify your username, password, and SMTP server details and make sure they are correctly configured. Follow these steps:

1. In Outlook 2013 and later, go to File > Info > Account Settings > Account Settings.
2. In Outlook 2010 and earlier, go to Tools > Account Settings.
3. Under the Email tab, click on your POP email account and click Change. You may also double-click to open more settings.
4. In the Change E-mail Account window, check and update the details, such as login username and password, and then click More Settings.
5. Under Outgoing Server tab, check the My outgoing server (SMTP) requires authentication option.
6. Select Use same settings as my incoming mail server and then click OK.
7. Restart Outlook for the changes to take effect. Then, try to send emails.

Solution 3: Verify the Port Number

Wrong port number can also lead to a failed connection with the mail server, resulting in the error 0x800ccc78. Follow these steps to fix it:

1. Open More Settings again (as in the above solution) and click the Advanced tab.
2. Check that the SMTP port number is correct.
3. If you are not sure or don’t know, contact your administrator to learn more about the right port number, and then enter it.
4. Click OK and then restart the Outlook.

Solution 4: Disable ‘Secure Password Authentication’

This option can sometimes interfere with outgoing emails. You can disable this option by following these steps:

1. In Outlook 2010 and earlier versions, click Tools > Account Settings. In Outlook 2013 and later, click File > Info > Account Settings > Account Settings.
2. Double-click your email account and then click More Settings.
3. Under the Security tab, remove the tick from the box – Always prompt for logon credentials. In the Servers section, uncheck Log on using Secure Password Authentication (varies based on your Outlook version).
4. Click OK.

Solution 5: Check and Install Latest Updates

Make sure your Outlook and Windows are updated to avoid any incompatibility issues or bugs that may have triggered the error. The steps are as follows:

• Open Outlook and click File > Office Account.
• Then, click on the Update Options.
• From the options, click Update Now.
• If new updates are available, download and install them immediately.
• Once installed, restart Outlook (you may also reboot the system) for the changes to take effect.

Similarly, open Settings > Updates & Security on your system and then check and install Windows Updates.

Solution 6: Check Conflicts with Other Programs

Outlook may conflict with other programs on your system, such as the antivirus, leading to the error 0x800ccc78. Follow these steps to troubleshoot the issue.

1. Disable your anti-virus or anti-malware temporarily. Then restart Outlook and check if the error persists.
2. If the error has been resolved, make sure to add Outlook and the PST file as an exception in the antivirus.
3. If this doesn’t work, contact the antivirus support for more help or install an Outlook-aware antivirus software.

Solution 7: Disable Add-ins

You can disable the add-ins in Outlook to see if they’re causing the error. To do so, follow these steps:

• Run Outlook in safe mode. For this, press Windows + R, type outlook.exe /safe, and press Enter.
• Go to File > Options.
• Click Add-ins and then click Go at the bottom, beside Manage Add-ins.
• Uncheck or clear checkboxes against all add-ins and click OK.

• Close Outlook Safe Mode and restart Outlook normally.

At this stage, check if the error 0x800ccc78 is fixed. If it did, enable one add-in at a time and review Outlook for the error. If the error appears just after activating a specific add-in, remove it immediately to resolve the error.

Solution 8: Repair or Reinstall Outlook

You may try to repair or reinstall Outlook to resolve the Outlook error 0x800ccc78. But first, back up your original PST file, which is located in the following location:

%localappdata%/Microsoft/Outlook

Then, follow these steps to repair the MS Office:

• Open the Control Panel and click Programs. Under Programs and Features, click Uninstall a program.
• Choose Microsoft Office from the list and click Change.
• Select the Repair option and follow the onscreen instructions to complete the repair process.
• Once the repair is complete, reboot the system.
• Open Outlook and check if the error 0x800ccc78 is resolved.

If this doesn’t work, reinstall the program. First, uninstall MS Office and then install the latest build. Sign in using your email account.

Solution 9: Create a New Outlook Profile

If the Outlook profile is corrupt, you can create a new Outlook profile and remove the old corrupt one. The steps are as follows:

• Close Outlook and open the Control Panel.
• Click on User Accounts > Mail.
• Click Show Profiles > Add.

• Type the name for the new profile and click OK.
• Follow the onscreen prompts and configure your email under this new profile.
• Once configured, go back to the Mail Setup window and choose your old profile.
• Click Remove and then click Yes to confirm.
• Start Outlook.

Outlook will load your new profile and create a fresh Outlook data file (PST). It will then download the mail items from the mailbox server. However, it will download only the latest emails or messages. To restore old messages, you need to repair the PST file and then restore the mail items to the new profile.

Solution 10: Repair Outlook Data File (PST)

A corrupt Outlook PST file can also trigger the Outlook error 0x800ccc78. However, you can use a built-in Inbox repair tool, also referred to as SCANPST.EXE to fix minor errors and inconsistencies in the PST file. The steps are as follows:

• Close Outlook and then open File Explorer.
• Go to the following location and find the PST file. 

C:\Users\<YourUserName>\AppData\Local\Microsoft\Outlook

• Copy and backup the PST file to another folder or drive.
• Then, navigate to the following location:

C:\Program Files\Microsoft Office\root\Officexx

• The path to the Office folder may vary based on the Outlook version and Windows edition.
• Double-click on the SCANPST.EXE program to run it.
• Click Browse and select the PST file for repair. Click Start.

• The tool will scan the PST file for errors and inconsistencies. It will show the errors and inconsistencies in the PST file, if any.
• Click Repair to start the PST repair process. This may take a while to complete.
• After the repair, start Outlook.

If the SCANPST.EXE fails to repair PST file, crashes or freezes during the repair process, you should use an advanced Outlook PST file repair software, such as Stellar Repair for Outlook. This advanced software can repair severely corrupt, encrypted, and large PST files of size up to 50 GB or more with complete integrity. It can save the recovered mail items in a new healthy PST file which you can import into your new profile and restore all the mail items via Outlook Import Export Wizard. In addition, you can also export all your mail items from a repaired PST file directly to Microsoft 365 or live Exchange Server.

Conclusion

Troubleshooting the Outlook error code 0x800ccc78 requires a systematic approach as explained in this guide. By understanding the common causes and implementing the suggested solutions, you can quickly fix the error 0x800ccc78 in Outlook and ensure smooth email flow. Remember to use an advanced Outlook repair software, such as Stellar Repair for Outlook, when the manual solutions or built-in utilities like SCANPST fail to fix the error or the issues

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