Error in Outlook Desktop: Cannot expand the folder.

This guide applies only to University of Chichester issued devices.

If you are experiencing this on a personal device please contact the Support and Information Zone.


This message is usually displayed because you have added a resource email account with user credentials rather than using our approved method of delegate access to access the inbox of the account. The full version of this message typically reads:

“Cannot expand the folder. The set of the folders cannot be opened. The file C:\Users\*Username*\AppData\Local\Microsoft\Outlook\*EmailAddress*.ost is not an Outlook data file (.ost).”  Illustrative image
Where *Username* is your username and *EmailAddress* is the resource account that you are trying to access.
If you are receiving this error when accessing your University email account and have no resource email accounts added to Outlook please contact the Support and Information Zone.

Resolution for University of Chichester issued devices

To resolve this issue you will need to remove the locally added resource email accounts.

  1. In Outlook, click File.  Illustrative image
  2. Then Account Settings and Account Settings.  Illustrative image
  3. Then select the resource email account and then select Remove Illustrative image
  4. Click Yes on the pop-up.  Illustrative image
  5. Close and re-launch Outlook.
  6. To access a resource email account please ensure you have completed both sections of the Managing another user’s mailbox or generic mailbox in Outlook article.


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