Iptables problem sending mails

Hi there

I got this problem for sending mails outgoing mi LAN:

mail log output:

Feb 11 17:53:50 e2kserver postfix/smtp[5034]: 506D5A803B: to=<recipient@gmail.com>, relay=none, delay=3786, status=deferred (Host or domain name not found. Name service error for name=gmail.com type=MX: Host not found, try again)</recipient@gmail.com>

I think my /etc/resolv.conf is ok, it looks like this:

search e2k.com.py
nameserver 200.85.32.2 (ISP DNS Server)
nameserver 200.85.32.3 (ISP DNS Server)
nameserver 127.0.0.1

Something I noticed is when I stop the iptables service the mails are sent, but when I start the iptables service again it doesnt work..

this is my iptables -L output:

Chain INPUT (policy DROP)
target     prot opt source               destination
ACCEPT     all  --  anywhere             anywhere
valid-src  all  --  anywhere             anywhere
ACCEPT     tcp  --  anywhere             anywhere            tcp spts:1024:65535 dpt:ssh state NEW
ACCEPT     tcp  --  anywhere             anywhere            tcp spts:1024:65535 dpt:http state NEW
ACCEPT     tcp  --  anywhere             anywhere            state RELATED,ESTABLISHED
ACCEPT     all  --  192.168.0.0/24       anywhere
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:domain
ACCEPT     udp  --  anywhere             anywhere            udp dpt:domain
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:pop3
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:ftp
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:ftp-data

Chain FORWARD (policy DROP)
target     prot opt source               destination
valid-src  all  --  anywhere             anywhere
valid-dst  all  --  anywhere             anywhere
ACCEPT     all  --  anywhere             anywhere            state NEW,RELATED,ESTABLISHED
ACCEPT     all  --  anywhere             anywhere            state RELATED,ESTABLISHED

Chain OUTPUT (policy DROP)
target     prot opt source               destination
ACCEPT     all  --  anywhere             anywhere
valid-dst  all  --  anywhere             anywhere
ACCEPT     all  --  anywhere             anywhere            state RELATED,ESTABLISHED
ACCEPT     tcp  --  anywhere             anywhere            state NEW,RELATED,ESTABLISHED
ACCEPT     all  --  anywhere             192.168.0.0/24
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:domain
ACCEPT     udp  --  anywhere             anywhere            udp dpt:domain
ACCEPT     tcp  --  anywhere             anywhere            tcp spt:domain
ACCEPT     udp  --  anywhere             anywhere            udp spt:domain
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:pop3
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:smtp

Chain valid-dst (2 references)
target     prot opt source               destination
DROP       all  --  anywhere             16.0.0.0/4

Chain valid-src (2 references)
target     prot opt source               destination
DROP       all  --  0.0.0.0/8            anywhere
DROP       all  --  ip-72-16-0-0.valornet.com/12  anywhere
DROP       all  --  92.168.0.0/16        anywhere
DROP       all  --  16.0.0.0/4           anywhere
DROP       all  --  40.0.0.0/5           anywhere
DROP       all  --  27.0.0.0/8           anywhere
DROP       all  --  0.0.0.0/8            anywhere
DROP       all  --  anywhere             255.255.255.255
DROP       all  --  169.254.0.0/16       anywhere

what could be wrong?