If your corporate security team blocks all direct outbound connectivity to port 443 and forces all traffic through a proxy, then how do you test a external website connection? Instead of using telnet and manually connecting to the proxy and then outbound, you can do it with a single one liner using Netcat.
nc -v -x192.168.1.10:3128 -Xconnect www.google.com 443
Here we specify our internal proxy address the port it’s listening on. Then we pass in the external server we wish to connect to. In this case google.com on port 443.
If all goes well you should get a connected message since we used the “-v” for verbose output.