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275946Re: Adjust smtp to limitations of a host

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  • Victor Duchovni
    Apr 1, 2011
      On Fri, Apr 01, 2011 at 09:20:39AM +0200, Ultrabug wrote:

      > > What happens if you happen to exceed the limit on particular host
      > > among the 10? If it just quickly returns a 4XX code, and does not
      > > penalize future connections, ignore this limit and let Postfix do
      > > what it does by default.
      > >
      > The result is pretty much that they deny any further email with 4XX
      > codes AND penalize further connections. It just stops accepting any new
      > mail.

      So instead of gently nudging you to the right sending rate, the DoS
      their service and require the whole planet to hand-tune transports for
      their domain, this is insane, and as much as possible, senders should
      not play-along with this insanity. I know that some senders will have
      to jump through hoops for business reasons, but if possible apply some

      > > Have you considered the less aggressive concurrency
      > > feedback controls in Postfix 2.5?
      > >
      > > slow_initial_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
      > >
      > This sounds interesting indeed, I didn't understand fully these
      > cohort/feedback options, I'll give them a try !

      This really won't help if the remote sites response to exceeding their
      maximum rate is a sticky refusal to accept further mail.

      If that's the case, you must psychically (i.e. prior hand-tuning) stay
      under their limits. The feedback controls assume that the feedback is in
      the form of transient 421 responses when the connection concurrency or
      re-use limits are reached. No simple feedback algorithm will dynamically
      adjust to a feedback control that goes from open to sticky-closed.

      > > and if absolutely necessary, in master.cf:
      > >
      > > slow unix - - n - - smtp
      > > -o smtp_connection_reuse_time_limit=30s
      > >
      > > (the remote side starts rejecting traffic consistently instead of
      > > sending 421 for the 100th RSET over a given connection).
      > Many tanks for your time and help

      You probably can't do much with my advice, when the receiving system
      is fubared, your options are limited.

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