[RFCI-Discuss] DSN listing of secureserver.net

[Alan Brown]

On Wed, 25 Oct 2006, Alan Brown wrote:

> > On 25.10.06 03:56, Alan Brown wrote:
> > > Which raises the issue that RFC 821/822 stats that HELOs need not bear
> > > any relationship to the actual hostname - as long as they're
> > > syntactically valid.
> >
> > where? Imho statement 3.5 of rfc821 says just the opposite.
>
> It says should. There are various valid reasons why they may not, such
> as hosts behind NAT gateways, etc.
>
> HELOs are best suited to sending host domain identification and not much
> more than that.

Rechecking RFC821 (3.5) supports my position and validates Hotmail's use
of "HELO hotmail.com". Bear in mind that the primary purpose of a HELO
is to prevent a host looping to itself.


  3.5.  OPENING AND CLOSING

      At the time the transmission channel is opened there is an
      exchange to ensure that the hosts are communicating with the hosts
      they think they are.

      The following two commands are used in transmission channel
      opening and closing:

         HELO <SP> <domain> <CRLF>

         QUIT <CRLF>

      In the HELO command the host sending the command identifies
      itself; the command may be interpreted as saying "Hello, I am
      <domain>".

[note the use of "DOMAIN" here and not "HOSTNAME"]

      -------------------------------------------------------------

                     Example of Connection Opening

         R: 220 BBN-UNIX.ARPA Simple Mail Transfer Service Ready
         S: HELO USC-ISIF.ARPA
         R: 250 BBN-UNIX.ARPA

                               Example 5

      -------------------------------------------------------------

      -------------------------------------------------------------

                     Example of Connection Closing

         S: QUIT
         R: 221 BBN-UNIX.ARPA Service closing transmission channel

                               Example 6

      -------------------------------------------------------------

August 1982                                                      RFC 821
Simple Mail Transfer Protocol