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Although this question has been asked before, there was no accepted answer (and the quality of answers was not good).

For one site where I send emails to, the "in queue manager" delay metric is (on average) 50 times greater than any other provider. However I am struggling to find a canonical (or even generic) explanation of what is happening during this window. That is my starting point for remediating the issue or at least mitigating its impact on the active queue.

My average delays:

delays=2057/10.25/0.35/0.36

The problem site:

delays=715/463.7/0.8/1.4

Specifically its the second figure - 463.7 causing the issue. Both datasets averaged over >10000 emails.

(I'm not concerned about the volume of deferred email and before anyone mentions DNS - according to the 2.3.13 release notes DNS lookups are reported in the NEXT metric).

symcbean
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  • Any errors in the /var/log/mail.log – Turdie Feb 20 '24 at 16:32
  • Yes - I'm sending a LOT of emails. But none relevant to the problem here. – symcbean Feb 20 '24 at 16:55
  • If I am understanding the question correctly, you have one MTA on one IP address using SMTP (ESMTP) connecting and sending messages to one MTA on one IP address? This ape admin would manually send a message (e.g, telnet) to see if anything weird happens. – Paul Feb 20 '24 at 17:06
  • How is the overall performance of the machine doing? Maybe review a couple of atop traces when the quene is high – Turdie Feb 20 '24 at 18:30
  • Monitored 24x7. Load less than 0.5/cpu, memory usage around 15%. Not my first rodeo. – symcbean Feb 20 '24 at 21:30

1 Answers1

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You may tweak the following config parameters

maximal_queue_lifetime, maximal_backoff_time, or smtp_destination_concurrency_limit

You could also install a local dns Resolver like unbound. By caching DNS queries locally, Unbound can reduce the time it takes for your mail server to resolve domain names. This reduces latency, which can improve the overall responsiveness of your mail server, particularly when sending emails to multiple domains.

Turdie
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    maximal_queue_lifetime is the limit on time spent in the deferred queue. Nothing to do with the active queue. maximal_backoff_time will influence how frequently mail is resubmitted - but thats not what I am trying to influence. smtp_destination_concurrency_limit may have some impact here - but I suspect you just copied and pasted a generic list of configuration items related to Postfix thropughput. I even warned you that DNS was probably not relevant yet you proposed it as a fix without any justification. – symcbean Feb 20 '24 at 17:32