I had issues with my 6500a disconnecting from the internet also. After several calls to HP with no satisfactory answers, I experimented by turning off the power save function and have not had a connectivity problem since.
Now, I need to address the issue of not being able to send to the printer from my main email account. I get a "rejected" message nearly immediately. I can send to the printer from a secondary yahoo account, so I am not totally dead in the water. I don't think HP guarantees receiving from every ISP.