On Tue, Sep 02, 2014 at 01:21:47PM -0400, Wietse Venema wrote: > Viktor Dukhovni: > > > > In the RFC editor queue as of 2014-08-29: > > > > https://datatracker.ietf.org/doc/draft-ietf-appsawg-nullmx/ > > Hmm. This text says: > > When a submission or SMTP relay server rejects an envelope recipient > due to a domain's null MX record, it SHOULD use a 521 reply > code [...] > > Both 221 and 421 are sent at the end of an SMTP session. Postfix > uses 521 for the same purpose: is is like 421 except that the client > should not retry. > > Maybe the draft can be modified.
It is rather late in the process, with the draft in the RFC Editor's queue the only chance to modify it is I think AUTH48, and the nature of the allowed changes is limited. Yes, the recipient and sender basic response codes are backwards, this is a bug. It should/could be 521 for rejecting a nullmx sender domain, but definitely not for a nullmx recipient domain. -- Viktor.