Malicious users can retrieve deleted email and try to make password reset to every popular sites and original owner will lost their website / app account.
Gmail Confidential mode allow G Suite users sending emails with expiration date, restrict to forward, copy, print, or download email content or attachments.
MacOS isn't associated with Linux in any way. What we call macOS nowadays is operating system developed by NeXT.Inc called NeXTstep and it based from BSD