How Does SER Differentiate A Proxy That Isn't Working From an Unreachable Site or Link Removed?

I am not sure how this works. Thanks to any/all who respond.

Thats actually the difficult part. Usually you make a connection to the proxy and move on to tell it what site it needs to connect. If the connection to the proxy fails, you know it. But there are situations when the proxy is having issues handling SSL and then you get an error and don't know if it was the proxy or the site.

Thanks, Sven.  I appreciate that you've cleared this up for me.