Mail sent to Postfix default accounts @localhost.localdomain is routed to Plesk Administrator’s email

Symptoms

• Plesk Obsidian running on a Linux-based operating system
• Postfix accepts emails sent to mailboxes that do not exist for the domain in the Plesk GUI and forwards them to the Plesk admin mailbox
• The emails appear to be regular spam and result in entries that are similar to the following within the /var/log/maillog:
  Aug 20 08:32:44 server postfix/smtpd[1216681]: B479747251: client=unknown[203.0.113.2]
  Aug 20 08:32:45 server psa-pc-remote[1923586]: B479747251: from=<[email protected]> to=<[email protected]>
  Aug 20 08:32:47 server postfix/cleanup[1213413]: B479747251: message-id=<[email protected]>
  Aug 20 08:32:51 server psa-pc-remote[1923586]: B479747251: py-limit-out: stderr: INFO:__main__:No SMTP AUTH and not running in sendmail context (incoming or unrestricted outgoing mail). SKIP message.
  Aug 20 08:32:51 server psa-pc-remote[1923586]: B479747251: py-limit-out: stderr: SKIP
  Aug 20 08:32:53 server psa-pc-remote[1923586]: B479747251: spf: stderr: PASS
  Aug 20 08:32:53 server psa-pc-remote[1923586]: B479747251: check-quota: stderr: SKIP
  Aug 20 08:32:53 server postfix/qmgr[4119497]: B479747251: from=<rand…