Users who access HeinOnline via proxy servers have reported a problem using Dropbox. We’ve determined that this is occurring because Dropbox does not recognize the domain of the proxy server within the HeinOnline application. We do have the ability to add proxy server domains to the Dropbox application in HeinOnline; we encourage users to contact us with their proxy domains as these will be added individually and will enable all users of HeinOnline to take advantage of this great feature! Please send your proxy domain to firstname.lastname@example.org.
In addition to having HeinOnline add your proxy domain to the Dropbox application, you may have to whitelist all Dropbox domains in your proxy server’s settings. Please visit here to view the list of verified Dropbox domains that should be whitelisted in order for Dropbox to properly communicate with your proxy server.