You can change the limit as shown below but it wont stop the mail notifications. It will add the IP to csf.deny file but the notification will be sent to you.

Steps to change Deny IP Limit:

1. Go to csf.conf file located in /etc/csf/csf.conf
2. Open with any editor and search for deny_ip_limit.
3. Change the value as required but the default is 200, to increase value install IPSET option and then enable it.
4. You can download the rpm package of IPSET and then install it.
5. To enable IPSET, search for LF_IPSET and change the value to 1.
6. Now its enabled and then you can increase above 200.

Note: Increasing the Deny IP limit more than 200 is not recommended since the server load may increase.