Install Postfix on failmaster.local so that Fail2Ban can send emails when it blocks stuff.
Install Postfix on failclient1.local so that Fail2Ban can send emails when it blocks stuff.
Install Postfix on failclient2.local so that Fail2Ban can send emails when it blocks stuff.
Install Postfix on failclient3.local so that Fail2Ban can send emails when it blocks stuff.
Install Postfix on failclient4.local so that Fail2Ban can send emails when it blocks stuff.