Hi Falko and Edge,
I did as suggested in the howto, and on the browser I get the message that "Mail sent.", but both mail.form and mail_php.log are empty.
I got the email inside(to a local email address) sent from "Administrator ISPConfig", but not when I changed to send to an address outside, but this is because our smtp-port is blocked from our internetprovider.
But the log's are empty.