How can I generate an NDR from a users mailbox without disabling their user account or deleting the mailbox?
I’m not sure what you’re trying to achieve. An NDR is a sign that something is wrong with email delivery, so things like filling the mailbox up would achieve the same result. In theory, you could try spoofing an NDR using a carefully-worded auto-reply rule. However, this would appear as sent by the target mailbox, not by the System Administrator or Postmaster.
