Emails are automatically forwarded to an unknown address

Symptoms

• All emails from one affected mailbox (e.g. [email protected]) are automatically forwarded to an unknown address (e.g. [email protected]). Records like this can be seen in /var/log/maillog:

  dovecot service=lda, [email protected], ip=[]. sieve: [email protected]: redirect action: forwarded to [email protected]

• There are forwarding rules set up in Roundcube: Log in to webmail.example.com > Settings > Filters.

Cause

The account is compromized, attacker created the forwarding via webmail.

Resolution

1. Immediately change the affected account's password to a stronger one:

• Log in to Plesk
• Navigate to Domains > example.com > Mail Accounts
• Select the affected mailbox and generate a new password or set one manually

2. Log in to the affected mailbox via webmail and go to Settings > Filters to remove the malicious forwarding rule.