On 7/19/2014 10:25 AM, Viktor Dukhovni wrote: > On Thu, Jul 17, 2014 at 06:06:42PM -0700, Dave Crocker wrote: > >>> It just designates non-sending domains, >> >> No, it designates non-/receiving/ domains: > > That's a bit of an under-statement, because, for example, > with the widely practived: > > reject_unknown_sender_domain > > restriction in Postfix, mail from nullmx domains *is* rejected, > so any that declare-themselves non-receiving become non-sending > in practice. If the draft suggests that nullmx domains might > expect to send mail will impunity, that would be misleading. > > In practical terms, if you don't receive, you can't send (that is > you can't use the domain in the SMTP return path). Sorry, no. 1. The return-path is not required to have any relationship to any another email field. 2. The semantics of nullmx make an assertion only about receiving. In fact, there are legitimate scenarios that include use of domains used for sending but not receiving, as the draft cites. The fact that some operational choices might not allow this scenario is a separate matter, outside of IETF specifications. d/ -- Dave Crocker Brandenburg InternetWorking bbiw.net