In order to fix Outlook email attachment problem, you can download the file from the message. For this, click on the File tab of the Outlook window and select the Add-ins option. Then, click on COM Add-ins. Then, click on the Manage button. Your email address will then open, and you can open the attached file. Once again, you should save the file. If you're using Microsoft Outlook, you can disable the COM Add-ins.
See also - https://emailspedia.com/unable-to-open-outlook-attachments/