what i've done so far (did not work)
Set-TransportConfig -ExternalPostmasterAddress <EmailAddress>
Would set it to a shared mailbox address and assign rights to it from your helpdesk/support mailbox for visibility.
You can also set it to $null and not receive any NDRs which is the default setting
Set-TransportConfig -ExternalPostmasterAddress $null
this did not work either:
https://docs.mithi.com/home/configure-microsoft-365-or-office-365-ndr-settings-for-vaultastic