On Fri, Mar 04, 2005 at 09:59:22AM -0500, Mark Shewmaker wrote:
My understanding is that mx mechanism's shouldn't include IP
addresses:
1. Since MX names must be domain names anyway, and
2. since in the context of spf, it doesn't make sense for IP's
to be listed under "mx:" as opposed to "ip4:" or "ip6", and
3. since the spec does refer to the right-hand-side being
a domain-spec.
Is this correct?
It is.
The reason I ask is because of:
$ host -t txt advanta.com
advanta.com text "v=spf1 mx ptr mx:12.40.127.100 mx:12.40.127.108 ~all"
Given that the two ip's listed are their mx hosts, it looks like they
could just as well use "v=spf1 mx ptr ~all"
Furthermore, when you resolve the IP numbers to names, you
get "mail-in.advanta.com" and "mail-out.advanta.com"
Let's assume for a moment that they did indeed aggregate
their outgoing mail and that they use one server only:
"v=spf1 ip4:12.40.127.108 ~all"
or
"v=spf1 a:mail-out.advanta.com ~all"
If the "mail-in" server serves as a backup:
"v=spf1 ip4:12.40.127.108 ip4:12.40.172.100 ~all"
or
"v=spf1 a:mail-out.advanta.com a:mail-in.advanta.com ~all"
or
"v=spf1 mx ~all"
The ptr mechanism is necessary only when they do indeed allow
every host with a name ending in advanta.com (such as
"host1.farm2.sales.internal.advanta.com") to send mail.
Most people don't need the ptr mechanism and it is expensive.
cheers,
alex