Proxy settings for AppStore
How do you get the appstore to work if your computer is sitting behind a proxy?
So this will work behind a proxy if the proxy is configured to not only allow connectivity to apple, but also allows connectivity to Akamai's Content Distribution Network....
I had this issue for several years because I couldn't guess what the Appstore was trying to connect to *outside* of apple, but eventually was able to get a "netstat -na" on my Mac while opening the Appstore with nothing else and found that besides connecting to *.apple.com it also connected to a bunch of akamai owned IP spaces.