Error when you add a PST or OST file on a non-local drive in Outlook 2016

Applies to: Outlook 2016Outlook for Office 365Outlook 2019

Symptoms


When you try to add a personal folder file (.pst) or an offline folder file (.ost) in Microsoft Outlook 2016, you receive an error message that states that the file can’t be opened. These may include:

  • Errors indicating that the PST file has an "invalid file name."
  • "Access denied" errors.

This issue occurs when the following conditions are true:

  • The version of Outlook 2016 is 16.0.7910.1000 or later (how to check).
  • The .pst or .ost file is not located on a local hard drive. For example, the file is on a removable drive or a network drive.

Cause


This issue occurs because of a change in the way that Microsoft Outlook 2016 works with file names and paths. That change can make Outlook 2016 unable to add .pst and .ost files from a non-local drive, which was previously successful.

Change details

Starting with build 16.0.7910.1000, Outlook 2016 makes a specific call to an operating system component to determine the canonical path. With the change, the GetFinalPathNameByHandle Windows API returns the normalized path to a file. In the case of a mapped drive, GetFinalPathNameByHandle converts the path into the Universal Naming Convention (UNC) format. When converting the path, Windows must traverse the entire folder structure of the path to build the final name. If there are insufficient permissions to any folder in the UNC path, GetFinalPathNameByHandle will be unable to return a normalized path. As a result, Outlook 2016 can’t add any .pst files from this location.

For example, suppose you have mapped drive P: to \\Server\Share\Retricted\Everyone and you want to add a .pst file from P:\MyData.pst. In this example, you have permissions to the "Everyone" folder in the path, but have no permissions to the "Restricted" or "Share" folder. In this case, Windows is unable to return the normalized path. As a result, Outlook 2016 can’t add the .pst file. After an administrator adds List and Read permissions for you to the "Restricted" folder, Windows can traverse the full path and return a normalized path to Outlook. Then you can successfully add the .pst file.

As a reminder, adding .pst files from a network share is not technically supported in Outlook 2016. While this workaround will allow you to add a .pst file to your profile, you take the risk of any performance or stability problems when you use the .pst file in an unsupported configuration. See Limits to using personal folders (.pst) files over LAN and WAN links (KB 297019) for more information.

Workaround


To work around this issue, copy the .pst or .ost file to a local hard drive, and then add the file in Outlook 2016.

What if the .pst or .ost file can’t be moved from the non-local drive?

You can try to continue to use the file in this unsupported configuration. In that case, you may want to contact the vendor that provides the network storage about potential changes that might allow the storage path to be successfully translated into a final canonical path by Windows.

Status


Microsoft is currently investigating this issue and will post additional information here when it is available.

References


More information on the GetFinalPathNameByHandle function, which is used by Outlook