Mailing List CGatePro@mail.stalker.com Message #104166
From: Mark J Strawcutter <mjstraw@iup.edu>
Subject: Re: Blacklist by DNS name [(host name is unknown)]
Date: Thu, 02 May 2013 11:55:43 -0400
To: CommuniGate Pro Discussions <CGatePro@mail.stalker.com>
"also mx without working ptr records can be blocked"

You never receive connections from MX hosts so there's nothing to block.

You might possibly receive a connection from a host that is dual-purpose, both MX for the domain and outgoing SMTP server, but it is not functioning as MX when it connects to you.

In case you haven't realized, the mis-use of MX to describe any and all smtp servers is a pet peeve of mine :-)

Mark

On 5/2/2013 11:41 AM, Juergen P. [core] wrote:
jaja for sure, SPFand other stuff, but spf is not used everywhere.

i am talking about  ptr-stuff , reverse connect,  blacklisting,
graylisting and other spam prevention methods in general.
i dont want to go in detail. in some cases senders without valid
ptr-hostnames are blocked.  furthermore client hosts which are trapped
by rbl depend on a valid hostname, also - so if an ip block is not
blacklisted and the ptr record is ok, then everything looks fine :-)
also mx without working ptr records can be blocked .. and so on...

nice weekend :-)


On Thu, 02 May 2013 10:57:45 -0400
  Mark J Strawcutter <mjstraw@iup.edu> wrote:
comments inline

Mark

On 5/2/2013 10:38 AM, Juergen P. [core] wrote:
an mx is not used for sending ? sorry i dont understand you.

An MX host is used for receiving mail addressed to a domain.  Many
domains maintain separate smtp servers for outbound mail.

if a server receives a mail it looks if the sending machine is allowed
to send for that domain ?
what do you mean ?

I don't see where I said that.

What you just described is what SPF is for.  This thread is
discussing if you should check to see that the sending server has
reverse DNS (PTR) record published.  Very different.




On Thu, 02 May 2013 10:04:53 -0400
  Mark J Strawcutter <mjstraw@iup.edu> wrote:
No, the issue in this thread is how the _sending_ server's DNS is
configured, not how a domain's mx servers' DNS is configured.

Mark

On 5/2/2013 10:01 AM, Juergen P. [core] wrote:
oh yeah, it is ..


On Thu, 02 May 2013 09:29:16 -0400
  Mark J Strawcutter <mjstraw@iup.edu> wrote:
Thanks, I'll check rfc2025 shortly

MX hosts are for receiving mail, so how their dns is set up (or
not)
isn't an issue here.

Mark

On 5/2/2013 9:08 AM, Juergen P. [core] wrote:
rfc 2505 -  it does not describe exactly but shows some cases..
so you
can assume that mx's ptr records should be set and valid for
hosts
sending and receiving mails.

kr



On Thu, 02 May 2013 08:48:37 -0400
  Mark J Strawcutter <mjstraw@iup.edu> wrote:
I am unaware of any RFC (or other "standard" for that matter)
which
encourages or requires such a check.  But I'm always
interested in
being corrected.

Our analysis (albeit many years ago) showed that benefit
would be
minimal and we decided the cost in false positive collateral
damage
outweighed that benefit.

Mark

On 5/1/2013 2:01 PM, Jeff Wark wrote:
I was just wondering how many people used the setting where
you
reject
hosts if they do not have a valid PTR record for the
connecting IP
address.

Is it a standard, accepted policy at this time to behave
that way
or is
it still something only AOL does?

-Jeff

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