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you may need to increase the main.cf ... destination_concurrency_limit from 20

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  • Donovan Bray
    I am seeing the following in the postfix logs, and we are having a delivery problem to blarg.com. However the destination_concurrency_limit reported at 20 took
    Message 1 of 1 , Feb 11, 2013
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      I am seeing the following in the postfix logs, and we are having a delivery problem to blarg.com. However the destination_concurrency_limit reported at 20 took my by surprise. I was under the impression we had already set it higher.

      Feb 11 12:36:08 email postfix/qmgr[23132]: warning: mail for blarg.com is using up 4001 of 4812 active queue entries
      Feb 11 12:36:08 email postfix/qmgr[23132]: warning: this may slow down other mail deliveries
      Feb 11 12:36:08 email postfix/qmgr[23132]: warning: you may need to increase the main.cf  smtp104_120_110_27_destination_concurrency_limit from 20
      Feb 11 12:36:08 email postfix/qmgr[23132]: warning: please avoid flushing the whole queue when you have
      Feb 11 12:36:08 email postfix/qmgr[23132]: warning: lots of deferred mail, that is bad for performance
      Feb 11 12:36:08 email postfix/qmgr[23132]: warning: to turn off these warnings specify: qmgr_clog_warn_time = 0

      We use sender dependent transport maps to allow our applications to send out the correctly plumbed sending-ip.


      smtp      inet  n       -       n       -       -       smtpd
      smtp104_120_110_27 unix  - - n - 150 smtp -o smtp_bind_address=104.120.110.27 -o syslog_name=postfix-app1 -o smtp_helo_name=mail-27.redacted.com


      root@email:/var/log# postconf -n | grep destination_concurrency_limit
      smtp_destination_concurrency_limit = 75

      root@email:/var/log# postconf -d | grep destination_concurrency_limit
      default_destination_concurrency_limit = 20
      lmtp_destination_concurrency_limit = $default_destination_concurrency_limit
      local_destination_concurrency_limit = 2
      relay_destination_concurrency_limit = $default_destination_concurrency_limit
      smtp_destination_concurrency_limit = $default_destination_concurrency_limit
      virtual_destination_concurrency_limit = $default_destination_concurrency_limit

      If I am understanding the implications correctly the currently set 'smtp_destination_concurrency_limit = 75' ONLY controls the limit for the smtp line in master.cf; it's not an inherited default for any 'smtp' service like we had assumed.

      If my intention is to increase all of the smtpYYY_YYY_YYY_YYY interfaces then I need to set 'default_destination_concurrency_limit = 20' higher. (and 75 is probably way too high) 

      OR create entries for the specific transports in main.cf like

      smtp104_120_110_27_destination_concurrency_limit = 30

      I'm assuming that over time we set it higher, and not seeing a negative effect kept increasing it, but there is almost no mail that goes out the default smtp interface, so we've been effectively running at a destination_concurrency_limit of 20 this entire time on all of our custom interfaces. 

      I also understand raising the destination_concurrency_limit isn't going to solve the deliverability problem; it will only correct our understanding and intent regarding the configuration of our default_destination_concurrency_limit for this and other interfaces.

      Is my resulting understanding correct?
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