Extracting those last drops of performance

[Steve Freegard]

On 06/05/10 20:02, Martin Hepworth wrote:
> If you're doing RBL at MTA stage then make sure you turn the RBL's off
> in Spamassassin as you're only wasting cycles. Given them a zero score
> in mailscanner.cf <http://mailscanner.cf>

I disagree with this.  RBL checks in SA are not the same as doing them 
in the MTA.

The MTA is only going to check the connecting IP address; whereas SA 
will check all the IP addresses in the Received headers based on your 
configured Trust path.  That can make a big difference in a number of 
difficult to catch messages and being as the MTA will have done the 
external IP lookup - this will be in the DNS cache and will not generate 
another lookup to the RBL should SA query the same IP.

The only time it's work disabling lookups in SA is for URI checks if you 
do those in your MTA and reject based on them.  But even then I usually 
don't do this for the same reasons; DNS caching will prevent look-ups 
directly to the RBL servers and if the queue was long enough for there 
to be a delay enough for the cache entry to expire - you might get hits 
on the same lookups that failed earlier as fresher data is available.

Regards,
Steve.