more efficient RBL checking

[Red Squirrel]

Right now way I'm setup is each time an email goes through my spam filter the RBLs are queried. While this does not really impact me much, I was thinking how it could get worse in the future as mail volume increases. Is there an easy way to cache RBLs and only actually update them every hour or so? Or from what I understand these are just DNS queries, so is me having a caching DNS server good enough?

 

[QuixoticOne]

A DNS cache ought to do the job well for any hosts behind it that use it for DNS queries.

For any SINGLE host I'd ASSUME that the typical DNS client implementation OUGHT to keep a local cache of most of / all of DNS query results for a time period up to the TTL (Time To Live) value of any received authoritative DNS result. Things like rebooting or free memory pressure might cause a local cache to be cleared prematurely of the record's TTL though.
I'd certainly be disappointed to find that a typical client doesn't cache the results for at least up to a few hours, though maybe I'm in store for some disappointment.

Anyway the point about TTL is that even a cacheing DNS proxy server should not / must not keep a record of DNS records for BEYOND the TTL specified in the authoritative DNS result, so take a look at the TTL values of the RBL responses and compare that number to the frequency of DNS query traffic your hosts generate for DUPLICATED queries that could potentially benefit from a cache and you'll see how much if any benefit you'll get.

 

[Red Squirrel]

ah cool.

Is there a way to configure bind to ignore TTLs lower then NN amount?

I mean, its not really an issue now, but I'm thinking more of the grand scale, like if my system was serving millions of emails per day, then it would be an issue.