While we focus on the content of the message, we also need to consider the visual impact. If you are able to choose your typeface, make sure that it conveys a professional image (e.g. Times New Roman, Georgia, Cambria, or Ariel). Using a font that is childish (e.g. Comic Sans, Kristen ITC, Freestyle Script) suggests that you are more playful than serious and that you are not particularly professional. A heavy font (e.g. Impact) will make you look pushy. This might sound silly, but there's a ton of research on the impact that typeface has on the reader's perception of the sender and of the message. Since an online class lacks face-to-face interaction, your students have nothing to go on but the words you write and what those words look like.