[Dovecot] need to block user by IP address (tried denyhosts, xinetd, iptables etc)

[David Ford]

I'm not a proponent of fail2ban as I think going straight to the horse's
mouth is wiser (keep it all in iptables in the first place).  I agree
with Stan that your VPS provider is on the wal-mart list.  If no other
solution avails, code up a quick little ditty that does the actual
socket listen.  If the incoming IP matches an allow list, hand it off to
dovecot as an exec(), if not, deal with it as you see fit - normally,
dropping the packet on the floor.

-david