There is a somewhat popular convention that if a domain publishes an MX like this:
whatever.example MX 0 . it means the domain does not receive mail. There was a draft about it in 2005 but it's never been formally standardized and the question has arisen how widely imlplemented it is. I don't see anything about it in the postfix docs. Does Postfix do anything special with such an MX? Or if not special, does it fail deliveries? R's, John
