Since you may never discover the rogue it is best to keep your emails of proper decorum or encrypted if they are of a sensitive investigative nature. Unencrypted email is not the vehicle for case reports or sensitive letters. One method to ensure proper decorum is to let your mother read the message. If she would send, it is most likely proper. Until everyone catches up with the current technology it is best to send email in plain text.
Many lists require plain text so that all members can read.
There is nothing worse than to spend a great deal of time composing the meaning of life and then finding that no one could read your HTML formatting. It's all about the content not the cover. Current browsers such as Netscape Communicator and Microsoft Explorer will allow you to read these types of emails. There are also special email programs on the market that can handle the latest in this technology. Attachments often require a special plugin or software so the recipient can read them.