DO NOT mark every message as urgent. Every message isn't urgent so reserve that level for when it is really needed. In short, don't cry wolf. DO NOT write anything that would embarrass you if it bacame public. DO encrypt documents that are of a sensitive nature.
Encryption adds another level of security to documents.
Using a face to face meeting or telephone call to convey the message. DO consider how you word your messages. DO save E-mail messages when necessary. Remember to use good filing habits or the messages could become lost in a sea of other E-mail messages. DO clean out your IN and OUT boxes.