This is pointless argument, please stop
There are those who think they are right in spamming people with reports
of a virus they didn't send and the rest of the planet who think they
are mad and wish they'd get a clue.
As the recipient of the DSN is _always_ the best
judge whether the DSN was sent to a forged return-path, why not take
advantage of that superior knowledge?
because that superior knowledge has already thrown them all away
without looking any slight chance of one being valid is wasted
If the AV systems that know they are dealing with forged senders, which
they do, just dropped them then the volume of potentially valid ones
may be low enough that we wouldn't just bin them all
If you make it hard we will ignore it.