It's documented and obvious in the csf.conf file. The official CSF GUI makes it even easier, if it's available to you.
DNA's repost of awsmonster documentation appears to spell things out for you, too.
Yes, very helpful. Obvious to you, maybe. not the person asking the question.
Official SCF GUI? in CWP? you mean the ugly-ass, unintuitive page with a stack of vertical blue buttons? lol.
anyway, for anyone still experencing this issue, i found this worked for me:
in cwp admin, search for csf
click on "CSF Firewall" in the search results
click "Firewall Configuration"
scroll roughly 1/3 down the text file and look for the headding "# SECTION:Reporting Settings"
first setting under that headding should be "LF_ALERT_TO" - remove the email address/s you no longer want alerted
save
go back to the "Firewall Configuration" page and click "Firewall Restart"