In the YPOP Configuration under the Advanced
Preferences----Proxies, there is a check box
to Connect to the Internet via HTTP proxy server.
However, if I check it, and only put in a HTTPS proxy,
and leave the HTTP Proxy host empty, it doesn't
take the changes.
My office network setup, only HTTPS proxy has to be
specified, HTTP is transparent. However, YPOPs
doesn't support having only HTTPS specified, it's either
both or none.