[winstonwinston]

> Finally, one aspect to consider is that many mail servers reject mail when the Envelope From domain has no MX or A/AAAA records. When the Envelope From domain and From domain are identical, this may reduce the number of relevant cases. The np tag was nonetheless introduced, so it was probably deemed realistic that a mail receiver reaches the point where the np policy is evaluated.

In practice DMARC verifiers can/will do the same for checking ‘non-existent’ subdomain. Query A/AAAA/MX and if no usable answers are given, the subdomain does not exist. Who cares if it is NXDOMAIN or NODATA.