I'm a little bit surprised that Microsoft created a migration tool for Sharepoint that doesn't work behind a corporate proxy (see official doc)?!
Proxy connections are not supported. Using Proxy connections yields errors such as "SharePoint login fail" or "cannot load document library".
I thought many of the Sharepoint Online users are enterprises that are all using proxies… Right now I cannot install it because of that, and even if I'm able to install it (with offline version that doesn't exist?!), it seems it won't work because of this network configuration.
Is there any known trick to make it work on a corporate network? I spent some time searching on the Web without any good result.