Some companies have a central Proxy server, and all out-going requests must go through to the Proxy Server in order to access the Internet.
In this case, you might have to config Proxyman to proxy all connections to this External Proxy.
You can config the External Proxy Setting by navigating to:
Tool menu -> Proxy Setting -> External Proxy Setting...
You can config the HTTP and HTTPS Proxy, which point to your external Proxy server.
Proxyman also supports Basic Authentication.