Re: Networking -- use of two Internet connections for one server with round robin DNS -- web okay, but should I do mail this way too?
Stan Hoeppner <stan@hardwarefreak.com> writes:
> On 7/9/2011 12:00 PM, lee wrote:
>
>> The rDNS check is very useful because it keeps out tons of SPAM without
>> occupying too many resources. It also seems to be common practise. Do
>> you have a better suggestion?
>
> Just checking for the existence of rDNS is no longer sufficiently
> effective against bot spam from infected residential hosts. This is
> because many/most? ISPs have rDNS for most of their IP addresses,
> whether dynamic or static.
Well, most rejects are because the HELO checks fail. There are only a
very few that fail because of the rDNS check. There isn't much SPAM
getting through; I'm getting less than one message per day.
> If you really want to put the hammer on residential bot spam, especially
> IPs that send to you before Spamhaus ZEN (CBL) lists them, and that are
> not listed in the various DNS dynamic block lists, then you need
> something like this:
Why would you use such lists and thereby have others decide what mail
you accept and what not?
> http://www.hardwarefreak.com/fqrdns.pcre
>
> This Postfix PCRE table consists of 1600+ rDNS patterns of residential
> broadband/SOHO ISPs around the world, and is extremely effective at
> killing bot spam, while putting very little load on your server.
Sounds like it must have taken quite some work to put the list together,
and it would need to be maintained. Won't graylisting work as well?
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