SORBS on autopilot?

Brian Keefer chort at smtps.net
Tue Jan 12 13:27:32 CST 2010


On Jan 12, 2010, at 10:48 AM, Dave Martin wrote:

> On Tue, Jan 12, 2010 at 11:51:47AM -0500, Jed Smith wrote:
>> On Jan 11, 2010, at 11:11 AM, Jon Lewis wrote:
>> The vibe I got from a number of administrators I talked to about it was "why
>> would a standards document assume an IPv4/IPv6 unicast address is a residential
>> customer with a modem, forcing those with allocations to prove that they are
>> not residentially allocated rather than the other way around?"
> 
> Because a default allow policy doesn't work in today's environment.

There are lots of other ways to deny that don't cause massive collateral damage.  Allowing IPs with "suspicious" PTRs to attempt a connection doesn't mean their mail is delivered, or even that their connection will succeed.  There are better ways to deny.

> Blocking generic and residential addresses is the single most effective
> thing we've ever done to reduce spam.

Not surprising, but at what cost of false positives?  Maybe your organization is different, but the ones I talk to are much more worried about missing a single e-mail than blocking an extra 1,000.

> Most legit senders don't want to look like a compromised box in
> someone's bedroom anyway.

There are literally thousands of companies who don't grasp the difference, or have little ability to influence their appearance.  I listen to the guy in the next cube over say "setup your RDNS" probably half a dozen times a day.  He's lucky if they even understand what he said most of the time.  Most people just do not grok DNS--even when they're given simple templates to fill out, cut, and paste they still manage to screw it up, or simply ignore it.

The membership of this list probably has one of the highest concentrations of DNS-clue in the world, but it's not representative of most organizations with an e-mail server.

--
bk



More information about the NANOG mailing list