Hi,
My config is as follows :
Internet - Ubuntu - Switch - LAN (few Windows machines & Ubuntu boxes)
My LAN is able to access internet, but my mail clients are not able to connect to the public IP to retrieve mails from externalmail server. Kindly help
Thanks

is port 110 to the outside open?
take a look at your firewall

A good pointer is to look at the error messages

is there a command i can use to check if port 110 is open or not

from the outside telnet public_IP 110

yes I think squid is allowing use of only port 3128. DO I need to add a similar line in squid.conf mentioning port 110
from an Ubuntu machine on my lan, telnet 192.168.0.1 110 was refused, but 192.168.0.1 3128 was allowed.

You need to telnet to the external ip from the mailsever at port 110

You need to telnet to the external ip from the mailsever at port 110

Hi,
But I am able to download mails onto my Ubuntu box which connects directly to the Internet. This has squid2.7 stable3 version, no firewall, no mailserver, no IPTables.
My LAN (consisting of 2Windows & 1Ubuntu) is able to browse the Internet, but not able to send/receive the mails which are being hosted by an external ISP.
My config is Internet - Ubuntu - Switch - LAN (few Windows machines & Ubuntu boxes). Do the mail clients on LAN need port110 to be open on squid to send/receive mails or does port 3128 suffice.
Should I telnet from LAN or from my Ubuntu m/c connected directly and should I telnet my static IP or the IP where my mails are currently being hosted.

login on a machine on your lan where you can not get mail
telnet to the external mailserver on port 110

Did you setup firewall rules to redirect traffic to port 110 to 3128 ?
should look like: