I have same problem, my iptables
Generated by iptables-save v1.4.7 on Tue Aug 25 17:32:40 2015
*filter
:INPUT DROP [0:0]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [131:33564]
:fail2ban-MAIL - [0:0]
:fail2ban-SSH - [0:0]
:fail2ban-VESTA - [0:0]
:vesta - [0:0]
-A INPUT -p tcp -m tcp –dport 8083 -j fail2ban-VESTA
-A INPUT -p tcp -m multiport –dports 25,465,587,2525,110,995,143,993 -j fail2ban-MAIL
-A INPUT -p tcp -m tcp –dport 22 -j fail2ban-SSH
-A INPUT -p udp -m udp –dport 25 -j ACCEPT
-A INPUT -p tcp -m tcp –dport 25 -j ACCEPT
-A INPUT -p tcp -m tcp –dport 22 -j ACCEPT
-A INPUT -p tcp -m multiport –dports 80,443 -j ACCEPT
-A INPUT -p tcp -m multiport –dports 21,12000:12100 -j ACCEPT
-A INPUT -p udp -m udp –dport 53 -j ACCEPT
-A INPUT -p tcp -m multiport –dports 25,465,587,2525 -j ACCEPT
-A INPUT -p tcp -m multiport –dports 110,995 -j ACCEPT
-A INPUT -p tcp -m multiport –dports 143,993 -j ACCEPT
-A INPUT -p tcp -m multiport –dports 3306,5432 -j ACCEPT
-A INPUT -p tcp -m tcp –dport 8083 -j ACCEPT
-A INPUT -p icmp -j ACCEPT
-A INPUT -s 162.243.247.66/32 -j ACCEPT
-A INPUT -s 127.0.0.1/32 -j ACCEPT
-A INPUT -p tcp -m tcp –sport 20 -j ACCEPT
-A INPUT -p tcp -m tcp –sport 21 -j ACCEPT
-A INPUT -p tcp -m tcp –sport 22 -j ACCEPT
-A INPUT -p tcp -m tcp –sport 25 -j ACCEPT
-A INPUT -p udp -m udp –sport 53 -j ACCEPT
-A INPUT -p tcp -m tcp –sport 80 -j ACCEPT
-A INPUT -p tcp -m tcp –sport 443 -j ACCEPT
-A INPUT -p tcp -m tcp –sport 110 -j ACCEPT
-A INPUT -p udp -m udp –sport 123 -j ACCEPT
-A INPUT -p tcp -m tcp –sport 143 -j ACCEPT
-A INPUT -p tcp -m tcp –sport 3306 -j ACCEPT
-A INPUT -p tcp -m tcp –sport 5432 -j ACCEPT
-A INPUT -p tcp -m tcp –sport 8080 -j ACCEPT
-A INPUT -p tcp -m tcp –sport 8433 -j ACCEPT
-A INPUT -p tcp -m tcp –sport 8083 -j ACCEPT
-A INPUT -p tcp -m tcp –sport 12000:12100 -j ACCEPT
-A INPUT -p tcp -m state –state RELATED,ESTABLISHED -j ACCEPT
-A fail2ban-MAIL -j RETURN
-A fail2ban-SSH -j RETURN
-A fail2ban-VESTA -j RETURN
did you add the MX records on your domain to the droplet and also in the vesta cp ?