Re: DNS Caching? - ReadList.com

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DNS Caching?
\ Jay Chandler (13 Mar 2008)
. \ Victor Duchovni (13 Mar 2008)

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Subject:	Re: DNS Caching?
Group:	Postfix-users
From:	Victor Duchovni
Date:	13 Mar 2008

On Wed, Mar 12, 2008 at 05:54:15PM -0700, Jay Chandler wrote:

> Howdy.
>
> Does Postfix cache DNS queries? If so, how is this governed?

It does not cache DNS queries in most cases. This is up to the caching
nameservers listed in /etc/resolv.conf. Only RBL lookups are cached,
and only for the lifetime of the smtpd(8) process that performs the
lookup.

> The big issue is "If I pick a cname as a relayhost, is it going to cache
> that lookup for a time, or is it going to slam the DNS server with one
> request per message?"

"slam" is unduly colourful language. A mail server should have a local
caching DNS daemon, and this daemon will be serving the cached data.
If your DNS cache is remote, the lookup latency will be higher.

--
Viktor.

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