fail2ban-systemd-0.9.3-1.fc23.noarch was installed on a clean fc23 build. The service did not start, with complaints to the journal as follows: fail2ban-client[13117]: ERROR Found no accessible config files for 'action.d/sendmail-whois-lines' under /etc/fail2ban Upon examination, the distributed rpm lacked the sendmail-whois-lines.conf file. Workaround: I grabbed the file from here and then was able to start fail2ban-system.service. https://github.com/fail2ban/fail2ban/blob/master/config/action.d/sendmail-whois-lines.conf
If you want to make use of the sendmail functionality in fail2ban you must also install fail2ban-sendmail.