Postfix fails to start: "postsuper: fatal: scan_dir_push: open directory deferred/X: Not a directory"

Issue

• The Postfix service fails to start or the postfix-script integrity check fails. The logs in /var/log/maillog or journalctl show an error similar to:

  Dec 19 05:04:47 localhost postfix[14498]: postsuper: fatal: scan_dir_push: open directory deferred/7: Not a directory
  Dec 19 05:04:47 localhost postfix/postsuper[14891]: fatal: scan_dir_push: open directory deferred/7: Not a directory
  Dec 19 05:04:48 localhost postfix/postfix-script[16908]: fatal: Postfix integrity check failed!
  Dec 19 05:04:48 localhost systemd[1]: postfix.service: control process exited, code=exited status=1
  Dec 19 05:04:48 localhost systemd[1]: Failed to start Postfix Mail Transport Agent.
  Dec 19 05:04:48 localhost systemd[1]: Unit postfix.service entered failed state.
  Dec 19 05:04:48 localhost systemd[1]: postfix.service failed.