Centos – Fail2Ban for sasl

[postfix-sasl]
enabled  = true
port     = smtp,ssmtp
filter   = postfix-sasl
action = iptables[name=SMTP, port=smtp, protocol=tcp, port=ssmtp]
logpath  = /var/log/maillog
maxretry  = 2
# 3 hours
findtime = 10800
# 24 hrs
bantime  = 864000

To change action from REJECT to DROP create file iptables-common.local in /etc/fail2ban/action.d/iptables-common.local
And insert

[Init]
blocktype = DROP

Original Link

Protecting SSH with Fail2ban