Re: design specifics --- the config label

Alan DeKok wrote:
> 
> Raymond S Brand <[email protected]> wrote:
...
> 
> > sources._email_.${DOMAIN}.            IN      PTR     ${PROVIDER1}
> >                                       IN      PTR     ${PROVIDER2}
> >
> > Each outbound provider lists the IPs that are authorized to send mail
> > (for one or more domains) using the same DNS method that DRIP uses;
> > only in the ``senders._email_'' space instead of the ``relays._email_''
> > space used by DRIP.
> 
>   Then the MTA has to walk all of the PTR records, to find out which
> of many providers is the one associated with the current SMTP
> session.  Not good...

Yes, one lookup per provider plus the provider list lookup, worst case.

How many domain names use more than one mail service provider for
outbound internet mail?

The alternative is that the domain name owner must somehow track what IP
addresses their providers use. The normal case is expected to be that
the domain name owner has exactly one provider.

The advantage to the providers with this scheme is that they do not have
to inform all of their customers when they add/remove MTAs; they just
make a simple change on their own DNS server. All of the customers using
the same MTA pool of a provider would point to the same ``senders._email_''
space of the provider and the provider would also control the TTLs there.

A variation would be to use MX RRs instead of PTR RRs and sort by priority,
but I've already witnessed enough MX RR religious wars.


Raymond S Brand