Found while working on T246559: Investigate CrashLoopBackoff Pods on 2020 Kubernetes cluster.
$ kubectl logs webarchivebot-backend-784564bb-7n8hl 2020-03-01 07:52:36 sh: 1: /usr/sbin/sendmail: not found Archiving... Connection to the DB failed: SQLSTATE[HY000] [1045] Access denied for user ''@'172.16.1.80' (using password: NO)
The Kubernetes environment does not include sendmail or a sendmail alternative binary. Instead Kubernetes tools should use SMTP directly via the mail.tools.wmflabs.org gateway. https://wikitech.wikimedia.org/wiki/Help:Toolforge/Email#Sending_via_SMTP