Hi,
> How should I configure my FreeBSD box to achieve this, what tools I should
> use?
You can only proxy traffic that the proxyserver itself understands. I
suppose that proxyserver from your ISP is an http proxy, so you have to
adjust your browser. You cannot proxy smtp or pop3, sip or whatever
through, let's say, squid. It doesn't understand any protocol other than
http (and ftp). Natting all outbound traffic to that proxyserver will not
work as you expect. There is ofcourse other proxyserver software that do
understand pop3, smtp, sip, etc etc but I don't think your ISP will
offer that service. Otherwise, give them a call and find out.
Hth.
Regards,
Robert