I am having problem in configuring my Squid Server.. Problem is that.. i able to access net through port 80 and the default ports tht are mentioned in /etc/squid/squid.conf file...

squid is proxy for HTTP(port 80), FTP(port 21) not for SMTP(port 25), POP(port 110). Opening SMTP port in squid is not advisable(read conf for why?).

I want to all my port open for two way communication.. Like as of now i am not able to connect thru..Kmail service...

Port control is done by firewall(man ipchains; man iptables). You need to open those ports. However, I find your question little unclear that if kmail is running on same machine or other machine on network. Most linux distributions have firewalls configured to allow outgoing connections. So Kmail should work if it is running on the same machine. Otherwise you need to setup your machine as a gateway.

Amish.