How can I stop sending NDR "Undelivered Mail Returned to Sender"

Virtualmin
1

Server has been added to a backscatter database. So I would like to disable the sending of NDR emails, specifically “Undelivered Mail Returned to Sender”

I have read various things online, and neither of these work:

  1. Adding this to /etc/postfix/master.cf

bounce unix - - n - 0 discard

  1. Adding this to /etc/postfix/header_checks doesn’t work (and header_checks is enabled in main.cf)
    /^Content-Type: multipart/report; report-type=delivery-status;/ REJECT no third-party DSNs
    /^Content-Type: message/delivery-status; / REJECT no third-party DSNs

So how does one just stop sending these please, so we can not be added to backscatter databases?

Thanks