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I think the only thing Reverse DNS and SPF prove is that
the Mail Admin knows how to set it up. Until a third party gets involved
to certify mail servers these settings are only confusing the system by
adding a false sense of security.
Correct me if I am wrong but aren't there three types of
reverse DNS checks.
1. Check to see if the sending server's
IP has a correct "A" record.
2. Check to see if the sending server is
listed in the MX record of the email domain.
3. As MXGuard does, check to see if any
of the IP addresses in the header resolve correctly.
As far as I am aware AOL only uses the first check.
The problem that you run into with checks two or three, is that if you relay
through a third party such as Postini the sending IP address probably will not
be listed in any of the MX records. And furthermore, the IP address
in the header could be the external/public address of a firewall.
As for SPF. Although it is required, a mail server
only checks if the SPF record is correct. If the SPF record does not exist
the SPAM scrubber/ Mail Server lets the email through and performs any
subsequent check that are configured.
With the amount of false positives you get with using
reverse DNS and SPF we found that you still have to deliver the mail with an
X-Spam header. Then ask the recipient to inform you when they see a false
positive so that you can enter it in you white list. Or add SPAM to the
Blacklist.
We have found that SPAM list such as Spamcop in conjunction
with Manually created list is the only sure way to curb SPAM. And feeling
comfortable with these list to do an auto delete.
Mike Odryna From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Dan Barker Sent: Wednesday, November 09, 2005 7:34 AM To: [email protected] Subject: RE: [IMail Forum] Reverse DNS Check If
that is the case, hurray! ("the same holds true for SPF").
That's
the purpose of SPF. It was never intended to prevent spam, and can't really,
because - as you've seen - spammers can set up SPF records as well. What it does
provide is the identity of the originating system. Now, with spam in hand and
the identity confirmed, you have the legal recourse to stop the
offender.
(unless it's overseas, of course).
Dan
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- RE: [IMail Forum] Reverse DNS Check Mike Odryna
- Re: [IMail Forum] Reverse DNS Check Rod Dorman
