On Jul 17, 2014, at 11:26 PM, Mark Andrews <marka@xxxxxxx> wrote: > 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. > > Just about everyone with a outsourced HTTP service needs to be able > to stop MTAs sending to email to the outsourced service. MUA's > could also lookup the MX RRset and issue a error without talking > to the MSA. I must be missing something here. You're saying you want me to set up a null MX for all my hosts to prevent someone else's MTA having undeliverable mail sitting in the queue for a week? Why would I care about your MTA's queue? Why would this issue even be on my radar? The second example you give, stopping mail being delivered to the web server, is actually served better by setting up a proper MX that directs the mail to the right server. Does an HTTP server really care about the occasional SYN to port 25? I'm not against this draft moving forward, but I find these use cases somewhat puzzling.