The cause appears to be the use of non-ASCII characters in file names. Microsoft describes it like so: “Any user may be ...

Microsoft is working to resolve a known issue that prevents some users from opening Excel email attachments in the new Outlook client.

There could be many possible reasons that could lead to attachment issues in Outlook. This includes incorrect Outlook settings, file incompatibility, incorrect mail format, etc. Try resetting Outlook ...

Are you unable to drag and drop attachments to your emails in Microsoft Outlook? Several Outlook users have reported that they just can’t attach files to their emails using the drag-and-drop method.

Microsoft has started looking into a problem that is preventing users from opening some Excel file attachments with non-ASCII ...

Email still plays an important role in sending important updates, sharing important documents, and mediating professional relationships. and sending important file attachments. In the Gmail app, you ...

There is a workaround, though.