[ On Thursday, October 23, 2003 at 16:42:17 (-0700), WJCarpenter wrote: ]
> Subject: Re: [Exim] Refuse connection if no MX for sending host
>
> gaw> Anyone too lazy or ignorant to configure the DNS for their
> gaw> mailers in this way is doing a disservice to the Internet
> gaw> community.
>
> What is the nature of the disservice in such cases?
Those without MX records for the domain names of every publicly
reachable and visible SMTP host are failing to identify to the public
that those hosts are indeed valid SMTP servers.
The use of the MX goes both ways -- i.e. both for sending and receiving
-- especially when one is trying to diagnose bounces that such a host
might return using its own hostname.
These days with the desire to validate sender addresses it's even more
critical that Internet managers make it easier for the public to
identify in the DNS what can and should be expected to be valid domains
in the sender addresses their systems might use; so in the case of mail
servers this means publishing MX records for all valid and authorised
SMTP speakers as well
Publishing MX records for all valid SMTP servers has been common and
recommended practice for decades, and it's the necessary first step
towards even more specific standardization of some means of identifying
all authorized hosts which might originate SMTP connections.
Personally for the purposes of validating sender addresses I've been
ignoring RFC 974's ancient backwards compatability rule for using A RRs
in mail routing for several years now and in general I have no problems
whatsoever with this policy. (Of course when it comes to actually
routing my outgoing e-mail I do still fall back on RFC 974 so that I can
still communicate to those sticks in the mud who would rather live in
the 1970's.)
After all, how the heck is John Q. Public supposed to tell the
difference between your mail server and your laptop, palm pilot,
toaster, or terminal server if you don't publish an MX record for your
mail server's own hostname!?!?!?!?
There is only false economy in not publishing MX RRs for all valid and
authorised SMTP hosts.
--
Greg A. Woods
+1 416 218-0098 VE3TCP RoboHack <woods@???>
Planix, Inc. <woods@???> Secrets of the Weird <woods@???>
