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Re: Site policy vs. HELO

2005-02-28 12:48:42

On Mon February 28 2005 12:44, Vince Sabio wrote:

I'm bringing this question over here from the SPAM-L list.

SMTP issues should be directed to the ietf-smtp mailing list; the
ietf-822 list deals with the Internet Message Format and MIME
extensions.  SMTP transaction questions are best handled on the
smtp list.

The following graf in RFC2821 appears to require an MTA (not an 
RFC2476-type MSA) to fall back to HELO for compatibility with older 
SMTP clients and servers):

    [QUOTE RFC2821 SECT 2.2.1]

However, it has recently been pointed out that the following graf in 
RFC2821 may permit sites to _not_ be required to fall back to HELO -- 
and issue a 550 response to HELO instead -- if local policy dictates:

    [QUOTE RFC2821 SECT 7.7]

So, the question: Is this a valid interpretation of Sect. 7.7 -- 
i.e., may an MTA provide a 550 response to HELO where it would 
otherwise have given a 250 response to an EHLO if the site policy for 
that MTA forbids HELO?

No. 7.7 does not mention HELO as a command to which such a response
may be issued.  The reason that servers MUST support HELO is that
there are still clients that do not support the newfangled EHLO.
EHLO is designed to be a backwards-compatible extension mechanism;
a server supporting EHLO can negotiate extensions with a client
which also supports EHLO; an older client supporting only HELO
must still be able to connect to a server and use the base SMTP
commands (i.e. w/o extensions).

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