~control/smtpclustercookie

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This file contains a cookie (random string) that is the same on all smtp MX clusters. It is to prevent outgoing mails looping back because of incorrect or faked MX records pointing to some external ip address which qmail-remote does not recognise as in reality 'itself' (as seen from the cluster perspective). The external ip address can be for example a load balancer or a NAT device.

Default: 

none

Example: 

cvkmd9078923hjv4nkd890q3g (Do NOT use this string in your setup!)

Notes:

  • String will be truncated after 32 characters.
  • If qmail-remote sees the same string advertised in qmail-smtpd greeting it will abort the delivery attempt, bounce the message and report a smtp loop error.
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