Mac App Store Submission troubles behind corporate network

An error occurred while connecting to the transport host https://itmsdav.apple.com: Operation timed out

Could not start delivery: all transports failed diagnostics

Last week we ran into a somewhat tricky issue when trying to submit one of our apps to the Mac App Store. Our group has already successfully submitted and updated three different apps, so this took us by surprise.

The errors returned by Application Loader, while a bit obtuse, smelled of corporate proxy or firewall. I assumed our authenticated corporate proxy was to blame, since lots of software doesn't play nicely with it -- error reporters, some built-in updaters, etc. Perhaps Apple had changed something on their end, who knows? 

Bypassing the proxy using the invaluable Authoxy didn't do the trick, nor did trying with Xcode 4's built-in tools. In fact, nothing worked until in desperation I  threw the app on my personal Mac and submitted it from outside our company network. Bingo. The upside is that the update is in review at the time of this posting. The downside is that nobody seemed to think much of my demand of having the company reimburse the cost of my MacBook :P


Next submission (when we're not up against a deadline), we'll have to get to the bottom of this with IT. Will update the post if I learn anything specific.
Update:
Since moving to another office location inside the same corporate network, we now get a different error. This one seems to eventually go through after failing a few times at 471 bytes.

com.apple.transporter.util.StreamUtil.readBytes(Ljava/io/InputStream;)