no need to do all these if u r using the POP n SMTP server address directly in your outlook (POP and SMTP) of mail service provider.

if u r running ur linux box as mail router and and using sendmail then u have to provide the (smart.smtp) server address

tell me one thing are u able to receive the mails??

if not then add the foolowing line in the iptable

-A RH-Firewall-1-INPUT -m state --state NEW -m tcp -p tcp --dport 110 -j ACCEPT
-A RH-Firewall-1-INPUT -m state --state NEW -m tcp -p tcp --dport 25 -j ACCEPT

then restart iptables service
this may solve ur prob.

or if this don't help u, try this command

service iptables stop (this stops the ipatble

just do it for testing.