I usually put in my course outline “Treat an email to your Professor as a professional communication”. Here I expand on that a little, to give you some pointers.
Before You Send an Email
1. Check if the information is in the Syllabus/Course Outline or is online on a Course Website. If it is, then you may not need to send the email at all.
2. Never send an email when you are angry.
3. See if your Professor has a policy on response time.
My personal policy is to respond within one working day. Don’t send multiple emails on the same subject every few hours. Give the Professor time to respond. (Yes, I am aware that some Professors are not good at responding to email!)
Once you have established that you need to send that email:
Use Your Institutional Email Address.
At my university this is a policy. We are not allowed to respond to students using personal email accounts, for privacy reasons. Even if there is no policy, emails from email@example.com or other fanciful email addresses does not fall under “professionalism”! It is best if you are clearly identifiable from your email address
Always use a meaningful and phrase relevant to the topic. You want the message to be seen and recognized. You do not want a spam filter to put it into a spam folder.
Address Your Professors by Title
Use “Dear Professor”, “Dear Doctor,” as the salutations. Some Professors like to be addressed by their titles — after all they earned them! You won’t offend anyone by using the titles. If your instructor is a woman, never, ever, use “Mrs” or “Miss”, as this denotes marital status, not academic status. Calling everybody “Dr” by default is a good policy. Some Professors do not insist on formality, but you should let them tell you what their preferences are.
Identify Yourself and Your Class
Write which class you are in, and which section/class time if appropriate. Many Professors teach several classes or sections at the same time, and they need to know who you are, so that they answer your question, without having to search for your name on class-lists
Your Query or Question
Keep it short and keep it organized. Ask specific questions, which can easily be answered.
Use of Grammar and Language
Use standard grammar and punctuation. Do not use texting abbreviations. This is not a text message you might send to your peer-group! Do not CAPITALIZE ALL THE WORDS. This is interpreted as shouting.
Sign off your email with “Thanks for your time”, or “regards”. Email is slightly less formal than writing letters, but still needs some polite way of signing off.
To my students. Do email me. Keep me informed. Tell me if you are having problems — not necessarily physics problems. If I can’t help directly, I can find out where to go for help