It seems that I am constantly having to explain to my students why writing matters. There is nothing more annoying than reading teaching evaluations at the end of a semester and seeing "This is not an English class -- why did he grade only based on how good we wrote?" (QED)
It is idiocy to believe that only English professors should be encouraging writing skills, so in order to pre-empt this blood-boiling criticism I address it headlong (I relish pointing out that our history department has published more books than our English department). And one of the ways I do this is to argue that in nearly every career that they choose they will have to write and that a huge percentage of that writing will come in the form of emails.
It might seem odd to equate writing a college essay with constructing an email. But the two really are not all that different. In both you are trying to make a point and eventually accomplish some goal. To be effective both must be clear, well organized, and well thought out. And in both cases the audience matters.
At his fine blog that is otherwise devoted to "research, international development, foreign policy, and violent conflict," Chris Blattman has a nice post that I hope gets as much attention as possible: "Students: How to Email to your Professor, employer, and professional peers." Students, and all of us, really, should commit his twelve rules to memory.