Hi
>> it takes less resouces to do the callback at rcpt than at the very
>> end of the spam filtering
>
> You could argue that using N lumps of somebody elses resources is worse
> than using 10xN lumps of your own. Especially if the 10xN is going idle,
> which on many systems it is...
we do really very few callouts, zoombies get detected before
reaching the callout check so we almost do not do callouts for
mail comming from non real servers, and for real servers without
spf and that are not whitelist we only do callouts until that
servers gets whitelisted, which is pretty fast if it's a real
server not doing weird things.
In the other hand, checking if a user exists or not should
be quite fast (we don't mind that other do callouts for our
domains, altough we use spf on all of them)
Anyway if you just want to prevent people doing callout for your
domains just publish spf records, it will not hurt.
--
Best regards ...
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David Saez Padros http://www.ols.es
On-Line Services 2000 S.L. telf +34 902 50 29 75
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