When I worked for an investment bank (over 2 decades ago), we wrote emails to a WORM storage device (I think from EMC) so it was literally impossible to acciden

When I worked for an investment bank (over 2 decades ago), we wrote emails to a WORM storage device (I think from EMC) so it was literally impossible to accidentally delete emails without physically destroying the device (which was backed up to tape and replicated to an identical device on the other coast). We retrieved sample emails quarterly to prove the device was working.