On Thu, Nov 27, 2014 at 03:40:21AM +0000, Viktor Dukhovni wrote: > You must have been napping upthread.
If still puzzled:
http://tools.ietf.org/html/draft-ietf-appsawg-nullmx-10#appendix-A.2
https://tools.ietf.org/html/draft-klensin-smtp-521code-02#section-4
--
Viktor.
