negative caching of throwaway spam domains

Barry Margolin barmar at
Thu Jun 22 00:03:16 UTC 2006

In article <e7bvl8$2eqm$1 at>, Ken A <ka at> 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?

What's the problem?  Don't you want spam to be blocked?  You'd prefer 
that it be blocked at the filter, but if not it gets blocked at the hub.

If you don't want filtering on the hub, why do you have it checking 
whether the sender domain exists?

Barry Margolin, barmar at
Arlington, MA
*** PLEASE post questions in newsgroups, not directly to me ***
*** PLEASE don't copy me on replies, I'll read them in the group ***

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