I have used the following commands
acl Safe_ports port 25 # smtp
acl Safe_ports port 110 # pop3
But when i configured my mail account in my client's machine it doesn't seem to work... Any suggestion....
Squid is a HTTP Proxy server. That means, HTTP only. There are some programs like "Proxifier" that intercepts packets from programs in Windows machines and uses the special HTTP CONNECT method to get that working, but it's a hack. Use have to put the ports in SSL_ports, not in Safe_ports to get this working.
Your mail client doesn't speak HTTP so you can't use an HTTP proxy.
Edit
To get "it working" you need to say what are you trying to achieve and why you're trying to use an HTTP proxy. Note that you cannot use Squid as an email proxy server.