Someone else gave me this answer to a similar question:
https://forum.pfsense.org/index.php?topic=88347.msg488730#msg488730
Only issue seems to be, that the line has to be added anew after each OS upgrade, or so it seems, but otherwise it does the trick for me.
So the first few lines of my /etc/crontab file now look like this:
SHELL=/bin/sh PATH=/etc:/bin:/sbin:/usr/bin:/usr/sbin HOME=/var/log MAILTO="" #minute hour mday month wday who command #You can easily edit the file with the Diagnostics > Edit File page.