When trying to send a contact form there is a report with the filled in form at the log, but the form isn't sent by e-mail. The log gives the following error:

Unable to send mail: mail(): SAFE MODE Restriction in effect. The fifth parameter is disabled in SAFE MODE
...
#5 /var/.../concrete/src/Controller/AbstractController.php(161): call_user_func_array(Array, Array)

Tried to change the mailsettings to manual in stead of the default settings, but without succes.
Tried to find something about SAFE MODE within the settings and made sure the files are writable and executable, but also without succes.