>This comment was added as a follow-on note. Sorry for not being clear. > >Accepting messages from a domain lacking MX records might be risky >due to the high rate of domain turnovers. Within a few weeks, more >than the number of existing domains will have been added and deleted >by then. Spammers take advantage of this flux. Unfortunately SMTP >server discovery via A records is permitted and should be >deprecated.
All it would require is a couple of large ISP's to adopt such a policy. "MX 0 <self>" really is not hard and benefits the remote caches. >Once MX records are adopted as an _acceptance_ >requisite, domains not intended to receive or send email would be >clearly denoted by the absence of MX records. SMTP policy published >adjacent to MX records also eliminates a need for email policy >"discovery" as well. Another looming problem. Better yet us MX records to signal that you don't want to receive email e.g. "MX 0 .". It has a additional benefits in that it is *much* smaller to cache than a negative response. It's also smaller to cache than a A record. Since all valid email domains are required to have a working postmaster you can safely drop any email from such domains. >Don't accept a message from a domain without MX records. When there >is no policy record adjacent to the MX record, there is no policy, >and don't go looking. > >-Doug >