Re: [Asrg] seeking comments on new RMX article

[Daniel Feenberg <[e-mail]>]

On Tue, 6 May 2003, Scott Nelson wrote:

> 
> rDNS does not support multiple domains.
> with rDNS, if you have two vanity domains you need two IP addresses.
> if you run an email service you might host hundreds of domains
> per IP.  So, yes, if you're one of those people it's a lot simpler,
> because you couldn't support rDNS at all.
> 

Is this right? Is there some reason many different MAIL FROM: host
names couldn't point to a single SMTP host? 

I think the receiving host looks up the domain name of the FROM address to
check that the connecting host is among the RMX records returned. It
doesn't look up the connecting host to see if the FROM address is listed.

Why has Vixie's similar proposal gotten no discussion here? He wanted to
overload existing MX records with the same information. In effect, 
receivers would accept mail only from hosts with MX records matching the
MAIL FROM address. If a sending domain wished to send from a host but
not receive mail to it, the MX record could be given a very low priority.
A minor advantage here is that BIND doesn't need to be changed. A larger
advantage is that many sites already send and receive from the same host,
so there is a "start up capital" of many millions of pre-configured
sites.

If the "very low priority" is specified in the standard, then there isn't
even any difficulty telling if an MX record is specifically for
verification purposes or not.



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