How to Fix the Error '0x800CCC78' in Microsoft Outlook?
While sending or receiving email messages in Microsoft Outlook, you may receive an error message that is similar to the one as shown in Figure 1.
Outlook error '0x800CCC78' generally occurs when the Outgoing Server Settings for your email is not configured properly.
To resolve this behavior follow the steps as mentioned below.
Go to 'Tools'>> 'Account Settings' as shown in Figure 2.
When the 'E-mail Accounts' window opens up, select the email account which need modification and click on 'Change' as shown in Figure 3.
Then click on 'More Settings...' as shown in Figure 4.
Click on 'Outgoing Server' tab in the 'Internet E-mail Settings' window and check the box 'My outgoing server (SMTP) requires authentication', and ensure that the radio-button 'Use same settings as my incoming mail server' is selected, as shown in Figure 5.
Click 'OK' to close the 'Internet Email Settings' window.
Note: Do not click the Test Account Settings... button to test the settings. This will fail.
Click on 'Next' and then on the 'Finish' button to close the 'Internet E-mail Settings' window.
Click on Close button to close the 'Account Settings' window. SMTP authentication has now been enabled.
Try sending yourself a test e-mail message to make sure it works.