tickets about brute force attacks

Hi,
I get a lot of tickets like
subject:
Brute-Force Attack detected in service log from IP(s) 185.222.209.14, 91.200.12.174, 91.200.12.218

content:
A brute force attack has been detected in one of your service logs.

IP 185.222.209.14 has 650 failed login attempts: exim2=650
IP 91.200.12.174 has 335 failed login attempts: exim2=335
IP 91.200.12.218 has 339 failed login attempts: exim2=339

Check 'Admin Level -> Brute Force Monitor' for more information
http://help.directadmin.com/item.php?id=404

with the same ip, why the system don't block them?
how can I stop it? or how to stop the tickets created about that?

thank you

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