(Yes, that's an operational issue - if they are harvesting and selling a list of known-good From: addresses on misrouted mail, this will eventually end up adding to spam - and that's operational)
Site Finder on its own added to spam; spam volumes increased as the number of "sender domain does not resolve" bounces dropped away. Also customers' sending addresses no longer underwent this simple sanity check as all domain misspellings resolved. Although a solution to that part may be a second wildcard: *.com. IN MX 127.0.0.1 Mailers changed to drop mail for hosts MX'd to 127.0.0.1 This would also fix even more spam -- as people are swamped by spam bounces they sometimes change their own MX to 127.0.0.1. So adding a 127.0.0.1 check to the nonexistent domain check would actually be useful on it's own and mean then wildcard A record wouldn't have the negative impact on email. But it would take some time for people to roll out new mailers/configs with the new rule if it was to be a solution. David.