I’m only looking to overwrite specific files not the whole enchilada.
I use BleachBit, only worthwhile thing Hillary provided in my life. I used to use CCleaner, but read they had security issues.
Question that I haven’t seen asked (or answered) yet. What program do you use for emails - if it is a standard Microsoft email client (Outlook, outlook Express, Microsoft Mail (old program abandoned years ago), Microsoft Mail (unrelated new program with a different mail) then all the emails are probably balled up in a single .pst file - deleting them will likely be an all-or-nothing exercise. If anything else, there are probably copies of them stored away on the internet somewhere that will never be forever gone. (And, indeed, there are, in any event, probably copies on an NSA controlled server somewhere; maybe here, maybe in England.) So you might as well give up on the thought that you can really do anything about emails except put investigators to some effort.
As for other files, there are likely solutions. I knew of one federal agency that had a commercial quality drill press with a hardened bit that they used for no longer needed hard drives. It seemed reasonably effective.