negative caching of throwaway spam domains

Dan Mahoney, System Admin danm at
Wed Jun 21 17:53:21 UTC 2006

On Wed, 21 Jun 2006, Ken A wrote:

> Hi,
> We have 3 spam filtering machines that each run a bind caching
> nameserver to help with rbl lookups, etc..
> After mail passes through these machines it goes to our mail hub.
> Every so often, a spam from a throwaway spam domain will get through the
> spam filtering machines to the mailserver hub. The caching nameserver on
> the spam filtering machine will be able to lookup the sender's hostname,
> so sendmail accepts it.
> But, sendmail, on the mailserver hub will bounce it back to the spam
> filtering machine with an error.. 'Domain of sender address
> jthlhiyue at does not exist'. (that one is from this am..
> registered yesterday by a spammer).
> The question is, is there something I can do to, other than telling the
> mail filter machines to all use the same instance of bind to avoid this
> happening?
> Also, a bit off topic, but it occurs to me that this kind of information
> is useful in spam fighting. Are there any rbls out there that list all
> domains registered in the last 48 hrs?

I would ask on the SpamAssassin mailing list, as those guys 
seem to be most aware of what's available (even if it's not SpamAssassin 
you're using, this is not a bad idea for a plugin and/or blacklist) -- 
however, generically RBL's work on IP address, not domains.  Given an IP 
address a.b.c.d, the domains is looked up, 
and if it returns a certain value, it's considered listed.

What you'd be more likely to look at is a SURBL -- which looks to block 
url's embedded in emails, and works on actual hostnames as opposed to ips.

Also, I should note that parsing the information with regard to how long 
ago a domain was registered is somewhat difficult, as at this point we're 
out of the realm of DNS and into the realm of WHOIS.  And whomever 
conceived WHOIS apparently did not feel that things like standardization 
and formatting (or even date-field order) were things that needed to be 
agreed upon.

There is a long-out-of-date perl module which was written by the GANDI 
registrar that was supposed to parse these things, and had a modular 
plug-in architecture, however even that has broken majorly on .org since 
that registry no longer uses referrals.


"There is no right and wrong, there is only fun and boring."

-Fisher Stevens, "Hackers"

--------Dan Mahoney--------
Techie,  Sysadmin,  WebGeek
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ICQ: 13735144   AIM: LarpGM

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