Just saw that...
# iptables -vn -L
Chain INPUT (policy DROP 4083 packets, 193K bytes)
pkts bytes target prot opt in out source destination
1426 177K fail2ban-postfix tcp -- * * 0.0.0.0/0 0.0.0.0/0 multiport dports 80,443,25,587,110,995,143,993,4190
1426 177K fail2ban-dovecot tcp -- * * 0.0.0.0/0 0.0.0.0/0 multiport dports 80,443,25,587,110,995,143,993,4190
1427 177K fail2ban-roundcube tcp -- * * 0.0.0.0/0 0.0.0.0/0 multiport dports 80,443,25,587,110,995,143,993,4190
1096 74126 fail2ban-ssh tcp -- * * 0.0.0.0/0 0.0.0.0/0 tcp dpt:22
315K 67M ACCEPT all -- * * 0.0.0.0/0 0.0.0.0/0 state RELATED,ESTABLISHED
2367 142K ACCEPT all -- lo * 0.0.0.0/0 0.0.0.0/0
31 1348 ACCEPT tcp -- * * 0.0.0.0/0 0.0.0.0/0 tcp dpt:80
49 2316 ACCEPT tcp -- * * 0.0.0.0/0 0.0.0.0/0 tcp dpt:443
451 25528 ACCEPT tcp -- * * 0.0.0.0/0 0.0.0.0/0 tcp dpt:25
23 1048 ACCEPT tcp -- * * 0.0.0.0/0 0.0.0.0/0 tcp dpt:587
20 912 ACCEPT tcp -- * * 0.0.0.0/0 0.0.0.0/0 tcp dpt:110
16 704 ACCEPT tcp -- * * 0.0.0.0/0 0.0.0.0/0 tcp dpt:995
694 39834 ACCEPT tcp -- * * 0.0.0.0/0 0.0.0.0/0 tcp dpt:143
86 4648 ACCEPT tcp -- * * 0.0.0.0/0 0.0.0.0/0 tcp dpt:993
47 2660 ACCEPT tcp -- * * 0.0.0.0/0 0.0.0.0/0 tcp dpt:22
149 11657 ACCEPT icmp -- * * 0.0.0.0/0 0.0.0.0/0 icmptype 8
Chain FORWARD (policy DROP 0 packets, 0 bytes)
pkts bytes target prot opt in out source destination
Chain OUTPUT (policy ACCEPT 5553 packets, 1493K bytes)
pkts bytes target prot opt in out source destination
Chain fail2ban-dovecot (1 references)
pkts bytes target prot opt in out source destination
1426 177K RETURN all -- * * 0.0.0.0/0 0.0.0.0/0
Chain fail2ban-postfix (1 references)
pkts bytes target prot opt in out source destination
1426 177K RETURN all -- * * 0.0.0.0/0 0.0.0.0/0
Chain fail2ban-roundcube (1 references)
pkts bytes target prot opt in out source destination
1427 177K RETURN all -- * * 0.0.0.0/0 0.0.0.0/0
Chain fail2ban-ssh (1 references)
pkts bytes target prot opt in out source destination
1096 74126 RETURN all -- * * 0.0.0.0/0 0.0.0.0/0
O_o So this 's why he didn't answer the requests.. When Default policy is DROP and 4190 is not explicitly ACCEPT the packets fly into the nirvana...
So next step: Howto configure fail2ban to simply ACCEPT packets on this port..? I do used fail2ban never before..