The firewall on my VPS appears to be preventing my site from sending email. It was working fine until the end of last month. My hosting provider (Webfusion) has been next to useless.

I am able to send email if I open INPUT ports 32768-65535, but not if these ports are closed. Why would this be?

I have the following rules in my firewall:

# sudo iptables -L
Chain INPUT (policy DROP)
target     prot opt source               destination
VZ_INPUT   all  --  anywhere             anywhere

Chain FORWARD (policy DROP)
target     prot opt source               destination
VZ_FORWARD  all  --  anywhere             anywhere

Chain OUTPUT (policy DROP)
target     prot opt source               destination
VZ_OUTPUT  all  --  anywhere             anywhere

Chain VZ_FORWARD (1 references)
target     prot opt source               destination

Chain VZ_INPUT (1 references)
target     prot opt source               destination
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:www
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:https
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:smtp
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:ssmtp
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:pop3
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:domain
ACCEPT     udp  --  anywhere             anywhere            udp dpt:domain
ACCEPT     tcp  --  anywhere             anywhere            tcp dpts:32768:65535
ACCEPT     udp  --  anywhere             anywhere            udp dpts:32768:65535
ACCEPT     tcp  --  localhost.localdomain  localhost.localdomain
ACCEPT     udp  --  localhost.localdomain  localhost.localdomain

Chain VZ_OUTPUT (1 references)
target     prot opt source               destination
ACCEPT     tcp  --  anywhere             anywhere
ACCEPT     udp  --  anywhere             anywhere

The VPS is running Plesk 10.4.4
(please ask if you require further technical information to help me)