Written is the only way to go.  Have all of them sign to acknowledge getting the instructions and maintain a copy in their personnel file.  Here are a few suggestions that a well-considered policy might include:  The Company’s policy regarding computer usage includes the right to:  a. Read messages,  b.  Monitor and review e-mail at any time, c. Restrict access to and distribution of e-mail, d. Prohibit distribution of e-mail that may violate equal opportunity or other federal laws, e. Restrict personal use of computers, f. Prohibit sending/forwarding chain e-letters, conducting gambling activities, and g. Prohibit dissemination of confidential information.