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Outlook – The message interface has returned an unknown error

When saving an email message to a network drive, I get the following error;

“The message interface has returned an unknown error.”

Instead of saving the message, a tmp-file is created on the network location. When I rename the tmp-file to .msg, then it appears to be the message that I tried to save.

How can I get rid of the error and have the message save directly as an msg-file?

This issue appears to be specific to running Outlook 2007 or Outlook 2010 on Windows Vista or Windows 7. It also appears to happen more often to network shares that are either part of a Distributed File System (DFS) structure or located on storage hardware which isn’t running on Windows like a dedicated NAS system.

The solution is to disable a feature called “Robustified UNC” via the Registry;

Outlook 2007 Key


Outlook 2010 Key


Value name: DisableRobustifiedUNC

Value type: REG_DWORD

Value: 1 turn to 0

While the registry key is located in the Word hive, it actually applies to Outlook (and other Office applications) as well. Due to its location, it could be required to close all open Office applications before changes to take affect (or simply restart your computer).


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