I'm currently examining the following patent proposing the use of mail quota. http://www.google.com/patents/about?id=mFrNAAAAEBAJ&dq=s... This patent is filed in 2000 and issued 10 years later ! In 2006 it was apparently extended to international. Does this mean the validity of the patent is 20 years starting from 2010, or is it from 2000 ? This is weird. Note that I'm in europe and don't know US patent particularities.
The quota is on the ongoing mail, not the storage. Many ISP are using this method to limit spams or virus propagation from their clients. I think google does it too.