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.

Every email provider comes with some limitations, and almost all of them have one thing in common – limited attachment size. It doesn’t matter whether you use Gmail or Outlook as your email management ...

As spotted by Bleeping Computer, Microsoft has published a new service alert related to Outlook. Labelled as issue EX1189359 and titled "Users may be unable to open Excel files attached to email ...