The customer needs something that works behind their customers corporate firewalls without changing existing firewall configurations.

Most firewalls allow HTTP based outbound requests, which is what the sending process does/involves, and also what the polling process does [it makes a outbound https request to a known URL etc].

So, there are no changes to existing firewall rules . e.g. if you can surf to a https website, you can use the web storage service for sending and receivng.

Yeah, I know this technically allows all kinds of nasties back down the wire to the polling system, but since its a secure link and only known "safe" files are going to be sent or received I think most customers will be happy with the concept.

Heck, most corporates would let their users surf to websites and download stuff [e.g. executable software] and the reality is that this is a more controlled version of that concept and the files we are talking about won't be executable in any case, and good virus checking should stop any nasties in any case.