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Re: [Asrg] RDynamic addresses
Brasil Telecom is one such sample of a large provider (65% of the latin american email traffic) who does not consistently assign static IPs and commercial broadbands.
In theory their assignments are like
201-xxx-xxx-xxx.fnscexxx.dsl.brasiltelecom.net.br for residential broadband and like 200-xxx-xxx-xxx.bsacexxx.e.brasiltelecom.net.br for commercial broadband.
Unfortunately this is no longer true it seems and you'll find them just mixed up. Even for real commercial broadband connections most of the times the rDNS entries are screwed up - either because the owner does not know/care or BrT messed it up.
To make matters worse, they sell their DSL service through partner ISPs which sometimes manage the rDNS entries. Go figure.
We even see frequently smaller companies which use residential DSL to run their own outbound mailserver and of course permanently get blocked.
cheers
Andreas Saurwein
On 1/27/06, Daniel Feenberg <feenberg at nber.org> wrote:
Of these only 874 (13%) had an existing RDNS that did not reek of dynamic
assignment. That is, did not include the strings "dsl", "dynamic", "dial"
or "pool" and did not have any all-digit components.
So by adding that test, it looks like we could dramatically reduce the
remaining spam burden we face. But I wonder why the DNSBLs don't do that.
I have seen the suggestion that many legitimate mailservers have such
addresses. Is this really true? I never see them in my own incoming mail,
and I don't have access to a more general sample of known good mail. Can
anyone here cite specific legitimate MTAs that have such addresses?
Presumably if you reject dynamic sounding addresses, then you have a
whitelist for some MTAs. Would you care to characterize it, or post it? Is
it all individuals hosting their own mail server, or do some firms and
ISPs make this mistake?
So, how does it work for you?
Daniel Feenberg
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