The key is to know your recipient is able to receive HTML mail before sending it. If you're not sure, do everyone a favor and set your mail program to send mail as plain text. The common reason given for this is that, online, uppercase indicates shouting. While this is true, it is not the number one reason why you should not use all uppercase. Any student of design or typography will tell you that humans rely upon the tops of letters to read.
Words have distinctive shapes that are formed by the contour of the tops of letters.
We read by identifying these shapes, not by identifying individual letters and then piecing them together into words. At times, it can be very difficult to determine a sender's demeanor from the text of their email. Always remember that text is unable to inherit tone, and you, the sender, need to do something in your message to identify your attitude. See C . That is, notice who is getting your messages.