[AusNOG] IPv6 reverse DNS and Mail ...

[Scott Howard]

On Sun, May 19, 2013 at 9:45 PM, Daniel O'Connor <doconnor at gsoft.com.au>wrote:

> I wonder how much spam you block by rejecting submissions from hosts with
> incorrect/unconfigured reverse DNS entries.
>

Enough to make it something worth doing.  The exact percentages will vary
depending on the type of spam being received, but double-digit percentages
of spam aren't uncommon.


> I also wonder how much ham you block incorrectly..
>

If blocking hosts with no reverse DNS - none.  Or at least, so close to
none to not care.  There are enough hosts enforcing the existence of  some
form of reverse DNS that anyone who doesn't have it is going to have
trouble delivering mail to a non-insignificant percentage of the internet.

If blocking hosts where DNS isn't configured "correctly" (forward matching
reverse, etc) then you will block some valid email. Exactly how much will
depend on who's sending you mail, but it's probably too high for most
people to turn this on.

If blocking based on the HELO hostname, then you'll block a lot of
legitimate mail.

  Scott
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