The next time you encounter the Outlook attachment failed error message, try to clean your recycle bin. If this doesn't solve the issue, try turning off your security feature on your computer. This will allow Outlook to read and open the file. If that doesn't work, try the next solution. Almost all of these methods work for most people. If one method doesn't work, you can always try the other.
See also - https://emailspedia.com/unable-to-open-outlook-attachments/
Few questions asked by Outlook users: