Internet Mail and HIPAA compliance

I am trying to find opinions on whether the rules regarding email in the HIPAA regulations (sections 164.306(a)(1), (a)(2) and (a)(4)) indicate that an organization should restrict access to Internet mail by employees.

On the surface it appears to me that permitting access to Internet email would be a viloation because the organization has no way to track and ensure compliance. e.g, what is to stop an employee from transmitting PHI in a Hotmail account and if they did how could you know?

My thought is to block access to those accounts. Does anyone have an opinion as to whether that is reasonable or not?