open iptables for sendmail

Dear Sirs,

I'm running a Server with redhat. I want sendmail to send local mails 
(e.g. from php-scripts, or from shell-scripts) to another 
e-mail-address, but I can't get iptables work properly.

I tried this configuration, but it doesn't work:

:INPUT DROP [50957:5396723]
:FORWARD DROP [0:0]
:OUTPUT ACCEPT [336966:250894376]
[0:0] -A INPUT -s 127.0.0.1 -p tcp -m tcp --dport 25 -j ACCEPT
[0:0] -A INPUT -s 10.40.26.2 -p tcp -m tcp --dport 25 -j ACCEPT
[0:0] -A INPUT -s 127.0.0.1 -p tcp -m tcp --sport 25 -j ACCEPT
[0:0] -A INPUT -s 10.40.26.2 -p tcp -m tcp --sport 25 -j ACCEPT
[0:0] -A OUTPUT -p tcp -m tcp --dport 25 -j ACCEPT
[0:0] -A OUTPUT -p tcp -m tcp --sport 25 -j ACCEPT

10.40.26.2 is the IP of the server. When I stop iptables, everything 
works fine, the mails are sent. When I start iptables, the mails don't 
come out of the box.

Can you help me?

Thanks in advance,

Martin Ramskogler