There's a fairly key difference you're missing here. For ADSP, each
domain publishes what it thinks is its own policy, so if you look at a
million domains, you have to guess about the competence of a million mail
On the other hand, if you use one or two published drop lists, you can
afford to look at them and choose ones whose administrators are
competent, without having to individually vet each entry.
Of course, I could also keep list of competent publishers of MX records.
Indeed you could. And if the collateral damage from trying to use inept
MX records were as bad as the damage from trying to use inept ADSP
records, you probably would.
NOTE WELL: This list operates according to