For reasons of confidentiality and any potential claims of misuse of company time and property, you are advised to make such communications in your own time, using your own equipment and email account. You should never assume e-mail remains confidential and would be well-advised to be cautious in terms of the information you send over the internet.
Employers commonly have policies designed to restrict the use of company e-mail systems: you should look in the staff handbook for the terms of the IT Equipment Policy.
However, you would probably have legal protection if you were preparing for a disciplinary or grievance hearing and consulting with the person who will be accompanying you. But again there is always a risk that e-mail will fall into the wrong hands.
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