Can't the overwriting sometimes be erased to reveal the earlier message? Isn't that what the RESTORE command does on a laptop?
@the_doc No. Restore/undelete software merely restores visibility to a file that has been marked for deletion, but which has not yet been overwritten (That's a bit simplistic, but generally true).
Most local email systems add another complication, as deleted emails remain (marked for deletion but rendered invisible) until the mail files are 'compacted'. Since the mail is generally kept within a single compressed file, when the file is 'compacted' the compressed file is virtually rewritten without the deleted emails. It is nearly impossible to find the bits and pieces on the disk
But if local mail is compacted and a typical free-space wiper is employed (even just writing zeros) there is damn little left. Use a government wipe, and it is pretty impossible to recover anything. And it is a pretty simple script and a couple tools away from automation.
That all excludes web mail and outlook/exchange based email, and doesn't consider web based or machine to machine backups (like when you back up your phone to your desktop or to the cloud) which all provide, or can provide off-machine backups which can be accessed.
Hope that is clear enough.
@DB
