Rich Kulawiec on 24 Oct 2016 14:54:48 -0700

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Re: [PLUG] Postscreen (another tool for helping to minimize the effect of spam)

On Mon, Oct 24, 2016 at 05:33:48PM -0400, Keith C. Perry wrote:
> That doesn't quite make sense. The DNS lookups are going to get cached. 


Yes. They are.  This is why I recommend running a recursive caching
resolver (that only responds to connections from localhost) on each mail
server, whether it's inbound, outbound, or both.  (Of course in larger
configurations, that recommendation gets modified a bit.)  How large
the cache should be depends on the operational characteristics of the
mail server -- in particular, on the diversity of sources and sinks for
SMTP connections.

This also makes it possible to readily utilize DNS RPZ in conjunction
with the mail system.

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