On Aug 8, 2005, at 10:17 PM, wayne wrote:
However, the ptr *does* count. This ptr lookup is not the same as the
one in 1) because it refers to easydns.com, not cox.net. Even if it
was the same, they would both count.
Thanks for the explanation Wayme, however that strikes me as
strange. As I understand the spec the number of mechanisms and
modifiers that do DNS lookups is limited to 10. But surely, since
any ptr mechanism after the first doesn't need to invoke an
additional PTR lookup, shouldn't they not count against the limit?
Multiple ptr mechanisms in a single SPF record presumably just cause
SPF to add the specified domains to the list of acceptable parent
domains for a single PTR lookup performed on the server IP address
(since this IP address doesn't change over the course of the SPF
record evaluation). In the case of my example, the DNS PTR lookup at
step 2 should be sufficient for all ptr mechanisms. Am I
misunderstanding something? Is an SPF implementation expected to
issues multiple identical DNS PTR lookups on the server IP address if
there are multiple ptr mechanisms?
-Richard