not sure about OSX but

https://www.google.com/search?q=fail2ban%20%22last%20message%20repeated%22

can give you the answer for Linux (Debian in particular with rsyslog)
resolution

-- 
Yaroslav O. Halchenko
http://neuro.debian.net http://www.pymvpa.org http://www.fail2ban.org
Postdoctoral Fellow,   Department of Psychological and Brain Sciences
Dartmouth College, 419 Moore Hall, Hinman Box 6207, Hanover, NH 03755
Phone: +1 (603) 646-9834                       Fax: +1 (603) 646-1419
WWW:   http://www.linkedin.com/in/yarik