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Outlook Express is the predecessor of Windows Mail that was present in the Operating System till Windows Vista. Many users consider it as a light-weighted version of Outlook, but they both are entirely different applications. If you are still using Windows Vista somehow, then you may be using Outlook Express. Now, Microsoft does not provide any user support for this application, and you will have to tackle each error on your own. If you have connected a POP account with it, then you can get the following error-

0x800CCC91 POP3 INVALID USERNAME – Invalid username or username not found

If you have already connected the account with the same username in Outlook express and it is still showing the error, you need to search for the possible reasons and best methods to rectify the error.


  • You have entered wrong/invalid user name.
  • Your anti-virus has been set to automatically scan emails during send/receive process.
  • Your mailbox might have been corrupted.


You can get rid of the 0x800CCC91 POP3 INVALID USERNAME – Invalid username or username not found error message in following ways:

  • Check if the user name you have entered is correct or not. If the user name is wrong, retype the user name. Check your account login details through webmail. If you have configured POP3 account (Gmail, yahoo mail..) then you can request for recovery of user name and password from the email provider itself.
  • If the anti-virus installed on your computer system has been configured to automatically scan incoming/outgoing emails then this problem is very common. Reconfigure the anti-virus settings to do not automatically scan emails.
  • Uninstall the anti-virus of your system and then check if the error still appears.
  • Take backups of your DBX databases and reconfigure the Outlook Express account profile.

Kernel for Outlook Express – DBX recovery software helps you recover emails from damaged DBX file by repairing it. While recovering emails, contacts, etc. from damaged DBX file, the software keeps emails formatting and properties as is. Therefore, you do not need to do any modification in recovered emails. With Kernel for Outlook Express to repair outlook express database, you can perfectly repair DBX files created in Outlook Express 4.0 and above versions.


The manual solutions for getting rid of the error do not guarantee a definite result. When you are assured that the Outlook Express file has become corrupt, then you need to use Kernel for Outlook Express. The software will recover the complete mailbox content and allows you to save them in the desired format. You can install it on Windows Vista and use it to repair the DBX files.

Kernel for Outlook Express
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