I know, but thats not relevant here, I'm concerned about whats on this particular machine...

I've ran both ccleaner and Active Kill Disk, and the problem persist. I can still recover the files with Recuva. There are thousands of eml files which apparently have been overwritten previously...

please correct me if I'm wrong, but wouldn't all of the above suggestions apply to the following:

a) wiping free space on a drive - which I have done with ccleaner (with these settings: 1 and 3...

I have never done a total format like that - will I still be able to reinstall windows after that? from USB or DVD?

If I want to completely and securely wipe my hard drive so that there is nothing recoverable left, will a clean win 10 install with formatting do this?

Or do I need to first use killdisk or...

I have some old files (mostly emails) I want to get rid of so that they are gone for good and not recoverable. These are files that I have deleted in the past non-securely by simply deleting them...