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Outlook Error 0x800ccc78 Unable Send Message - Problem and Solutions

Updated on July 15, 2015

The message encountered during this error is: “Unable to send the message. Please verify the e-mail address in your account properties. The server responded:550 is blacklisted.”

Common Reasons For 0x800cc78 Error

Although there are many reasons for the error 0x800ccc78, the most causes of error are:

  • If your PST file is stored in drives which is having bad sector then, displays the error 0x800ccc78 and also will denote Outlook is in corruption state.
  • The error occurs when the system is overloaded with invalid reference.
  • Improper maintenance of PC causes error 0x800ccc78.
  • If your PST file is corrupted then, while sending the emails error 0x800cc78 message will be displayed.
  • Error can even occur because of the improper closing of the MS Outlook.

Furthermost Steps To Clear The Error 0x800ccc78

On receiving the error 0x800ccc78, the user should check whether the sender address. The sender address should be the full email address and not the username alone. The format should be ‘’.

When the error occurs, check out the following;

  • Make sure there are no leading or ending spaces to overlook types in your address.
  • Verify the authentication of sending is correct or not on the Outlook Server tab.
  • Check the address entered in the ‘From’ field is correct or not.

Steps to Overcome Errors

  1. Go to ‘Tools’ in Outlook and click on ‘Account Settings’.
  2. Double click on the email account accordingly.
  3. An Internet E-mail Setting window will appear.
  4. Select ‘More Settings’ and click on ‘Outgoing Server’ tab.
  5. Tick on ‘My outgoing server SMTP requires authentication’.
  6. Click on “Ok” button.

However, even after the settings if error is showing then, user need to go for third party for help.

Other Causes for Error 0x800ccc78

There are many reasons for the error 0x800ccc78 including registry errors, spyware, RAM decline, malware, etc. Let us see some of the causes.

  • Freezing of PC

    PC freezes when the whole system responds to the inputs. To overcome this, usually rebooting of the machine is preferred.
  • BSoD

    It stands for Blue Screen of Death, caused by fatal system error and ultimately it will end up in system crash.
  • Windows error

    This error occurs when unexpected condition occurs and leads crash of program or freezes the programs.
  • Virus

    The virus makes problem to the programs that are running in the system. Even if we get rid of it by anti-virus software, doesn’t mean it is completely error-free.


Although MS Outlook works well as desktop mail client, there are error codes seen due to some reasons such as malware, virus, etc. Error 0x800ccc78 occurs because of invalid email address. It is not username or password that must be entered in the address field, full mail address is necessary. There is some property provided by the Outlook to get rid of the errors. However, there will be a limit for it. So, the user will have to lend the help from third party-software.


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