This article describes the procedure for resolving the Outlook Express error 0x800CCC78. The instructions compiled here are reliable and correct to date. However, you must follow them carefully to avoid encountering Outlook Express problems.
The Outlook Express error 0x800CCC78 occurs when your email address is rejected by the SMTP server. The rejection can happen due to an invalid or incorrect recipient (email address), incorrect Outlook Express setup, and damaged Windows files among others. You can easily and quickly fix the error using this free Outlook Express support manual.
Open Outlook Express if it is not already opened. Click on the Tools tab and choose Accounts. When in the Internet Accounts window, click to highlight the Mail tab (highlight it only when it's not already highlighted). Click to select your email profile and then press the Properties button. When in Properties, click on the Servers tab. Check the incoming & outgoing mail server settings. If they seem to be wrong, erase them and enter correct ones.
Verify that your account name, which is your full email address and password are typed in correctly. Typo mistakes often create such problems. Make sure that the Log on using Secure Password Authentication (SPA) box is not checked. If it is checked, click to uncheck it. Check the My server requires authentication. Now hit the Settings button. Check the radio button beside Use same settings as my incoming mail server. Erase and retype your email address and password in the relevant boxes. Check the Remember password field and hit the OK button to close the Settings dialog box.
You will now return to Properties. If you want to verify whether other settings are correct or not, click the Advanced tab and look through them. Make necessary changes. When done, hit the Apply button and then OK to save and close the Properties window. Close Outlook Express and reopen it. Create a test mail and send it to yourself or any other email address.
If the error occurs when you try to send an email to a recipient, use this fix. Check that the recipient's email address is spelt properly without any comma, space, or full stop in the Reply To field. Often you ignore checking this small thing because you routinely send emails to that particular email address. So, remove the email address from the Reply To field and retype it correctly. Now send a test mail to that email address or to yourself. The email should go now without any problem.
If no above mentioned method works and the error persists, restore your computer to an earlier time. Here is a word of caution for you before doing the system restore. Remember that any recent changes like a new add-in or program install or updates install will roll back. Thus, you will have to reinstall any such application or updates after restoring your computer.
Make sure that you are logged in as an administrator to your computer. If not then log off and log back in as an administrator. When done, click the Start button and browse to All Programs> Accessories> System Tools> System Restore. Select a date or time and hit Restore. When prompted, confirm the action. Wait for the computer to roll back the changes. When prompted, restart your computer and get going.
If you are unable to resolve the error by yourself, contact an Outlook Express support or Microsoft technical support service.