If you've been in education in the last ten years, then you've received the subject-less email lacking a greeting and demanding "What I miss in class?" category of emails from students. A colleague of mine got an email once with no body but just the subject "About my D."
Truly we need to help students with the various modes of communication essential to life success and the ways to use them appropriately. Initial emails should be complete and formal with clear subject headings, progressional greetings and end salutations, and standard paragraphing. From there forward, follow the lead of the teacher, I tell students. If she responds without intro or outro salutations, then mirror that in your response. If she remains formal with "Dear X" and "Sincerely Y," then stay formal and follow her example.
Last week I got a half-dozen emails requesting college letters of recommendation for rising seniors. They were smart to ask early (before the end of their junior year!), but a couple never saw me in person, and one basically sent a text under the guise of an email: "Would you write a positive letter of recommendation for me? Sent from iPhone."
A quick Google search reveals countless templates for how to ask for a recommendation letter. After all, students may not have ever asked for something like this before and they may not realize the time it takes for teachers to write one well. Yes, it is the professional duty of high school teachers to write these letters when appropriate, but helping students to ask properly now will save them grief when they ask college professors for professional references or former bosses for a work referral.
To help students meet teachers halfway, I designed a Google Form that asks a requesting student to reflect on his time in my classroom. It's my way of saying, Yes, I will write a good affirming letter on your behalf, and I want it to reflect the specific ways you are a strong writer, reader, thinker. The questions require narrative replies in the form of specific stories from their class experience. These responses jog my memory and help me sort the 135 student experiences I shared during the previous year. I wonder if anyone else uses a form like this or has ways I could enhance it.