Check if IP is blocked by firewall:
iptables -L -v -n | grep 1.2.3.4
7769 409K DROP all -- * * 1.2.3.4 0.0.0.0/0
Find chain with:
iptables -L -n | less
Remove IP:
iptables -D fail2ban-sasl -s 1.2.3.4 -j DROP