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When I originally setup the Prometheus/Grafana architecture, I evaluated the various exporters and dashboards available which could replace the ones that typically ship with Munin (which is a lot), in #30028 (closed). I naturally gravitated towards the postfix_exporter because it is packaged in Debian but, as it turns out, that package has a number of issues:

• some metrics are missing, particularly the number of rejected/bounced emails out going (which is critical for our needs, e.g. #33037 (moved))
• it hasn't seen a release since feb 2020, over two years ago

So let's see if we can find an alternative to at least get rejection rates and better health metrics.

Launch checklist:

• adapt the mtail program to our needs, requires:
• make it work with our metrics (small patch)
• add queue tracking to node exporter (hack, but makes us totally free from the postfix exporter)
• deploy and test mtail on crm-int-01
• make or adapt Grafana dashboard to mtail program
• deploy and test on eugeni
• deploy everywhere