The useful part of an NDR is not the friendly text but the technical block: the reporting server, the recipient and the SMTP status such as 550 5.1.1 User unknown. It tells you which server in the chain rejected the message and why.
5xx codes are permanent (hard bounce), e.g. unknown recipient or a policy rejection. 4xx codes are temporary (soft bounce); the server keeps retrying and sends a delay notice after a few hours.
Backscatter happens when a server first accepts spam and then sends a bounce to the forged sender address. The right approach is to reject undeliverable mail during the SMTP dialogue.
Example
550 5.1.1 <max@example.com>: Recipient address rejected: User unknown in virtual mailbox table