In article <20140718032611.7B87E1A7B838@xxxxxxxxxxxxxxx> you write: > >There are lots of machines which do not have the SMTP port configured >yet have A or AAAA records resulting in a implicit MX record and >week+ long no delivery notifications. Right. That's exactly, precisely, the problem that null MX is intended to address. >The alternative to this is to remove the implicit MX record >construction from SMTP and make the presence of MX records mandatory >for SMTP. I'm sure there will be many more complaints about doing >that than adding a explicit no service record. That would be fine with me, but I hear it's 30 years too late, even for IPv6. R's, John