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Re: Adjust smtp to limitations of a host

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  • Victor Duchovni
    ... The number of 421 responses is not a good metric for success. The real metric is the resulting average time in the queue for messages that are finally
    Message 1 of 16 , Apr 3, 2011
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      On Sat, Apr 02, 2011 at 06:59:42PM +0100, Mark Alan wrote:

      > > > /etc/postfix/master.cf
      > > > slow unix - - - - - smtp
      > > > -o syslog_name=postfix-slow
      > > > -o smtp_connection_reuse_time_limit=30s
      > > > EOT
      > > >
      > > > /etc/postfix/main.cf
      > > > slow_initial_destination_concurrency = 2
      > > > slow_destination_concurrency_limit = 15
      > > > slow_destination_concurrency_failed_cohort_limit = 5
      > > > slow_destination_concurrency_positive_feedback = 1/5
      > > > slow_destination_concurrency_negative_feedback = 1/8
      >
      > > (...) You can certainly try, and report your findings.
      >
      > Tried the above setup. It does not help.
      > We have much more 421 with this approach than we had with our former
      > setup.

      The number of 421 responses is not a good metric for success. The real
      metric is the resulting average time in the queue for messages that are
      finally delivered.

      A dymamic feedback mechanism that is able to go faster, will necessarily
      elicit 421 responses at a stead rate, to keep it from reaching peak
      capacity. Naturally, a statically hand-tuned configuration that stays
      under the remote caps will not elicit 421 responses, but it is likely
      to stay below the optimal throughput.

      With sites whose 421 responses are NOT "sticky", the feedback controls
      will in a variety of cases lead to a nearly optimal throughput with
      some messages retried at a second MX or deferred, but the overall
      delay can be smaller than conservative upper-bounds on concurrency
      and message rates.

      --
      Viktor.
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