As you can see, the mail is send by the root user.
Received: by [HIDDEN].nl (Postfix, from userid 10025) id 022856000A9;
From: Cron Daemon <root@[HIDDEN]>
To: [HIDDEN]
Subject: Cron [HIDDEN] /usr/local/psa/admin/sbin/fetch_url '[HIDDEN]' > /dev/null
Content-Type: text/plain; charset="UTF-8"...