Local email messages on a Plesk server are not delivered: Found DMARC record contained a bad token value

Symptoms

• Local emails sent between mailboxes on the same domain are not delivered.

• Errors like below can be found in /var/log/maillog file:

  dmarc: Wrong the essential DMARC policy parameters for 'example.com': 'Found DMARC record containd a bad token value'
  dmarc: DMARC: REJECT message for mailbox2@example.com
  postfix-local: STOP during call 'dmarc' handler
  postfix-local: message discarded by a mail handler

Cause

Incorrect value is set to  _dmarc.example.com record on Domains > example.com > DNS Settings page.

Resolution

1. Log into Plesk.
2. Check/set correct parameters for the DMARC record for example.com or set it back to the default value:

v=DMARC1; p=none