I am not able to understand your question at all. Are you in charge of HR or any department head ? Performance of employees mean what ? Is it about good performance or bad performance ? to whom do you want to write. It will be like drafting any other email. If you are good at English, you can write anything you want. Your query needs further clarification. Am not sure about drafting an email or how to write to senior people. In official communication, that too internal communication, does not require any special writing. You mention the facts of what you want to write. Be objective in your writing. Be clear in what you want to communicate. That is all.