On January 17, 2010 12:37:46 PM -0800 "Daniel V. Reinhardt"
<crypto...@yahoo.com> wrote:
A proper ISP and Host would have the proper PTR Records set up thus
validating the said sender as being part of a reputable ISP or Host.
I am a "proper" host with a "proper" ISP. Yet I do not have a PTR record
for this particular IP. That doesn't make my mail server any LESS valid.
My previous smtp host was also a "proper" host with a "proper" PTR however
it was simply a DHCP address on a microwave wireless link. The presence
of the PTR record didn't make my mail server any MORE valid.
In neither case is/was the ISP in a position to vet the validity of my
mail server, except to the extent that they get abuse reports of course.
(Which has nothing to do with whether or not a PTR record exists.)
I would argue that the spf record I maintain validates my mail server
much more than any PTR record, yet rejection based on PTR record seems
to not let (at least some) mail servers even get to the point where
they would validate my spf record.
On January 17, 2010 3:16:54 PM -0600 Stan Hoeppner <s...@hardwarefreak.com>
wrote:
Rejecting mail due to lack of a PTR is an anti bot spam tactic. It is as
OK that much I do know. :) I think that has been the case since nearly
the beginning of the Internet, but at that time not as an anti spam filter.
prevalent today as it was 5 years ago, but probably less effective. Many
ISPs went PTR crazy, assigning them to all their dynamic consumer IP
ranges. DULs and generic PTR regexes are now more effective in this
regard. Even so, there are still large amounts of consumer IP space
without PTRs, so this tactic is still valid, and still widely used.
My point exactly, and I apologize for not being more forthright initially
but I wanted to draw out some answers without pointing anyone in a
certain direction. It seems the spam argument is the only argument.
You seem to be arguing both points of view simultaneously; one that ISPs
have gone PTR crazy so you can't trust the existence of a PTR as any
kind of signal, and the other that there are many cases of missing PTRs
and hence it is useful.
I would agree with the first point, ISPs are PTR crazy and why not -- a
PTR doesn't indicate anything other than that an ISP wants a name
associated with an IP -- very useful for diagnostics, but at the same
time I don't see how this validates (or rejects) a host as being a
real mail server
I don't follow your second point at all -- because some ISPs don't assign
PTR records makes it a useful filter?
My five years ago reply earlier was based on the effectiveness of
content-based spam filters. Five years ago (maybe longer) we didn't
have good content-based filters. Today they are not so terrible. I'm
not sure that the PTR record was ever a useful filter but given the
content filters of today, I don't think it is anymore.
I've also given up on SAV (sender address verification). Although
technically it should be absolutely required regardless of its spam
filtering capability (if you can't receive a bounce I won't accept
your message, thank you and goodbye), too many idiots out there have
misconfigured systems and I don't want to reject their mail. Some
battles you just can't win.
Sorry to go on and on and I can see this thread has degraded so let's
call this the end of it.
-frank
