If it should be that simple than i wonder why it is stated differently in documentation:
You can test the sending of emails easily with the
~/bin/mail). The corresponding configuration file is~/etc/mail.rc. The best way to test this is as a site user, since the notification scripts will later run with the same permissions.
And exactly whith that command i can send email without any need for additional installed software. So it could be much easier than depending on “sendmail” - checkmk delivers all necessary binaries! So my question is, why does checkmk does not use this tool when correctly configured?