Sending an email is appropriate if you are unable to reach the professor by phone or in person, if you need to send or receive an electronic document, or if you must have a copy of your conversation. If you need an immediate response, the issue requires long explanation that the instructor may have questions about, or the issue is confidential, do not use email. Verify that your question is not already covered in your course materials, and avoid sending email to request copies of notes or to say you will miss class. Get a new email address to use if your current one is inappropriate for business correspondence.
Put your name in your email address or the subject line. Include the course title and section or time, and key words about the topic in the subject line so the professor clearly sees what and who the email pertains to. Open the body of the email with a greeting using the professor's name -- correctly spelled -- followed by a comma. Explain the situation as succinctly as possible, as you would in a business letter. Avoid emoticons, slang and abbreviations such as "U" for "you." Use capital letters only when appropriate. Sign off with appropriate language as well, such as "Thank you," followed by your name. Proofread to be sure your message is clear.