On the other hand, draft-ietf-drums-smtpupd-06.txt has this to say:
Server implementations MUST support VRFY and SHOULD support EXPN.
For security reasons, implementations MAY provide local installations
a way to disable either or both of these commands through
configuration options or the equivalent. When these commands are
supported, they are not required to work across relays when relaying
is supported. Since they were both optional in RFC 821, they MUST,
if supported, be listed in the response to EHLO if service extensions
are supported.
On Fri, 10 Apr 1998 12:08:21 -0700 Dan Wing
<dwing(_at_)cisco(_dot_)com> wrote:
See http://pobox.com/~djb/surveys/smtpextensions.txt. You missed ONEX,
VERB, and VRFY. There are also lots of X extensions that should be
documented.
RFC1869 seems to indicate that VRFY is required and thus doesn't need
to be advertised in an EHLO response.
That is correct.