Nico Kadel-Garcia wrote:
For the 'ptr' mechanism to match, the reverse lookup does not have to
correspond to the forward lookup, but the forward lookup has to
correspond to the reverse lookup.
Does it? Can you point to that in the spec, please?
Section 4.6
Otherwise, J. Random mailhoster who has never published anything other
than a PTR and TXT record for outgoing.jrandomdomain.com, must also
create an A record or an MX record for outgoing.jrandomain.com.
Yes, if he has "ptr:jrandomdomain.com" in the SPF record, then he must have
an A record for outgoing.jrandomain.com that points back to the IP address.
In the DNS world, PTR's can be published by domains and IP address
ranges not owned by domain they point to!
But these domains cannot publish an A record that points back to the IP
address because they don't own the domain they point to.
It seems that the 'ptr' mechanism is the least understood mechanism. So
please read section 4.6 and then read it again.
"ptr:example.com" is the list of the IP addresses pointed to by A records in
the example.com zone and that have a PTR record that points to example.com.
Roger