fail2ban/config/filter.d/courier-smtp.conf

# Fail2Ban filter to block relay attempts though a Courier smtp server
#
#

[INCLUDES]

# Read common prefixes. If any customizations available -- read them from
# common.local
before = common.conf

[Definition]

_daemon = courieresmtpd

failregex = ^%(__prefix_line)serror,relay=<HOST>,.*: 550 User (<.*> )?unknown\.?$
            ^%(__prefix_line)serror,relay=<HOST>,msg="535 Authentication failed\.",cmd:( AUTH \S+)?( [0-9a-zA-Z\+/=]+)?$

ignoreregex = 

# Author: Cyril Jaquier