I have seen this issue all over the internet, but no solutions have worked for us.  It has been at least ~30 weeks since we first experienced this.  

I also posted this in the TechNet forums for Office 2016, but was directed here.  https://social.technet.microsoft.com/Forums/office/en-US/73f0225c-36d2-4bfd-be92-793b6efd3db6/error-opening-office-file-email-attachments-in-protected-view?forum=Office2016ITPro 

We use Windows Live Mail for email and have Office 2016 Home and Business.  If we receive a Word or Excel file email attachment (.doc, .docx, .xls, .xlsx) from an outside source and attempt to open it from the email, Word and Excel throw error messages and will not open the files.  

The error message in Word reads "Word experienced an error trying to open the file.  Try these suggestions [...]."  The error message in Excel reads "Microsoft Excel cannot open or save any more documents because there is not enough available memory or disk space. [...].

This issue appears to be directly related to Protected View.  Disabling Protected View results in the files opening without issue.  Keeping Protected View enabled but first saving the files to the desktop (or similar local location) results in the files opening without issue.  So there are no issues with the files themselves.  

A recent development is that if the program (e.g. Word) is opened first and then the email attachment is opened, the file successfully opens in Protected View.  So this would seem to indicate that Protected View does work, but something at launch is failing.

We have tried all suggested solutions posted around with no luck:

1. As noted above, disabling Protected View allows the files to be opened.  This is not a solution.  We need the protection of Protected View.
2. We cleared all temp files.
3. The system has plenty of free hard drive space and RAM.
4. We have tried repairing Office multiple times, using both Quick Repair and Online Repair.  Neither has helped.
5. We have kept current with updates.  I just ran the latest update today.  We are presently on Version 1609 (Build 7369.2038).  None of the updates over the past many months has helped.
6. We are current with all Windows updates.

If there is something that we have not tried, please let us know.  Otherwise - can we ever expect a fix for this issue?