Plesk emails are automatically forwarded to an unknown address

[senthil]

Symptoms

• All mail from a Plesk email address is forwarded to an unknown email address, with these records logged to
  /var/log/maillog:
  
  Code Select Expand
  dovecot service=lda, user=john.doe@example.com, ip=[]. sieve:
msgid=618dad9e22271@example.com: redirect action: forwarded to
unknown@example.com
• There are unknown forwarding rules in Roundcube (webmail.example.com > Settings > Filters)

Cause
The account has been compromised; the attacker created the forwarding rules in webmail.

Resolution
Secure the account and remove the forwarding rules.

• Set a stronger password for the affected account
• Log in to the affected mailbox in webmail
• Go to Settings> Filters and remove the malicious forwarding rule(s).

To help prevent such issue, harden the Plesk server: How to secure a Plesk server